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  • SAS Expanders vs Direct Attached (SAS)?

    - by jemmille
    I have a storage unit with 2 backplanes. One backplane holds 24 disks, one backplane holds 12 disks. Each backplane is independently connected to a SFF-8087 port (4 channel/12Gbit) to the raid card. Here is where my question really comes in. Can or how easily can a backplane be overloaded? All the disks in the machine are WD RE4 WD1003FBYX (black) drives that have average writes at 115MB/sec and average read of 125 MB/sec I know things would vary based on the raid or filesystem we put on top of that but it seems to be that a 24 disk backplane with only one SFF-8087 connector should be able to overload the bus to a point that might actually slow it down? Based on my math, if I had a RAID0 across all 24 disks and asked for a large file, I should, in theory should get 24*115 MB/sec wich translates to 22.08 GBit/sec of total throughput. Either I'm confused or this backplane is horribly designed, at least in a perfomance environment. I'm looking at switching to a model where each drive has it's own channel from the backplane (and new HBA's or raid card). EDIT: more details We have used both pure linux (centos), open solaris, software raid, hardware raid, EXT3/4, ZFS. Here are some examples using bonnie++ 4 Disk RAID-0, ZFS WRITE CPU RE-WRITE CPU READ CPU RND-SEEKS 194MB/s 19% 92MB/s 11% 200MB/s 8% 310/sec 194MB/s 19% 93MB/s 11% 201MB/s 8% 312/sec --------- ---- --------- ---- --------- ---- --------- 389MB/s 19% 186MB/s 11% 402MB/s 8% 311/sec 8 Disk RAID-0, ZFS WRITE CPU RE-WRITE CPU READ CPU RND-SEEKS 324MB/s 32% 164MB/s 19% 346MB/s 13% 466/sec 324MB/s 32% 164MB/s 19% 348MB/s 14% 465/sec --------- ---- --------- ---- --------- ---- --------- 648MB/s 32% 328MB/s 19% 694MB/s 13% 465/sec 12 Disk RAID-0, ZFS WRITE CPU RE-WRITE CPU READ CPU RND-SEEKS 377MB/s 38% 191MB/s 22% 429MB/s 17% 537/sec 376MB/s 38% 191MB/s 22% 427MB/s 17% 546/sec --------- ---- --------- ---- --------- ---- --------- 753MB/s 38% 382MB/s 22% 857MB/s 17% 541/sec Now 16 Disk RAID-0, it's gets interesting WRITE CPU RE-WRITE CPU READ CPU RND-SEEKS 359MB/s 34% 186MB/s 22% 407MB/s 18% 1397/sec 358MB/s 33% 186MB/s 22% 407MB/s 18% 1340/sec --------- ---- --------- ---- --------- ---- --------- 717MB/s 33% 373MB/s 22% 814MB/s 18% 1368/sec 20 Disk RAID-0, ZFS WRITE CPU RE-WRITE CPU READ CPU RND-SEEKS 371MB/s 37% 188MB/s 22% 450MB/s 19% 775/sec 370MB/s 37% 188MB/s 22% 447MB/s 19% 797/sec --------- ---- --------- ---- --------- ---- --------- 741MB/s 37% 376MB/s 22% 898MB/s 19% 786/sec 24 Disk RAID-1, ZFS WRITE CPU RE-WRITE CPU READ CPU RND-SEEKS 347MB/s 34% 193MB/s 22% 447MB/s 19% 907/sec 347MB/s 34% 192MB/s 23% 446MB/s 19% 933/sec --------- ---- --------- ---- --------- ---- --------- 694MB/s 34% 386MB/s 22% 894MB/s 19% 920/sec 28 Disk RAID-0, ZFS 32 Disk RAID-0, ZFS 36 Disk RAID-0, ZFS More details: Here is the exact unit: http://www.supermicro.com/products/chassis/4U/847/SC847E1-R1400U.cfm

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  • Why do I bother with RAID 10 ?

    - by GrumpyOldDBA
    Before I post anything I just want to clarify what I mean by RAID 10 , this is sets of mirrored pairs that have been striped as against a RAID 0 which has been mirrored. I've just had a disk failure in the data array for one of my dev servers, it's an eight disk raid 8, no real worries, replace disk and off we go - but no - the HP engineers told me from the diagnostics ( done to ensure I got the right replacement under warranty ) that not only had a disk failed but I'd lost all the data...(read more)

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  • Impossible to install Ubuntu 10.10 dual boot with Windows 7 on new Acer desktop computer

    - by Don Myers
    My brother has a brand new Acer Desktop with Windows 7. I have done many installs (40+) of Ubuntu starting with 8.10, and have never run into this. I've spent three hours trying to do a dual boot install of 10.10. When you get to the place where you normally would choose to install as a dual boot or overwrite the existing information on the hard drive, that block is just blank. Nothing. No choices even to do a manual partition setup. If you try to go on you get the message "No root file system is defined. Please correct this from the partitioning menu." but there is nothing in the partitioning menu. I tried a good 10.04 disc also. Same thing happens with it. I ran a gparted live cd, and it shows the hard drive as sda with 3 partitions on the original. sda1 is a small partition called PQService. sda2 is another small partition called System Reserved, and GParted says it is the boot partition. sda3 is the main partation with the operating system (Windows 7) and all of the empty space. There is a little unallocated space at the very beginning and very end of the hard drive. If I go to places in the Live CD, it shows a 640 gb hard disk called Acer, but it also shows a 640 gb hard disk called system reserved. They are the same disk. There is just one hard drive. If you click properties in the System Reserved 640 gb, it shows all information as unknown. I had to change the boot order in the bios in order to run the live cd. The hard drive instead of being listed as such is listed as Raid:Raid Ready. Something the way this computer is set up is preventing Ubuntu from being able to identify the hard drive partitions at all to do an install, even if you were not doing a dual boot and just wanted to overwrite Windows. Is this a bug that needs reported? This is a major problem for me and my brother, but also for Ubuntu if new users want to Ubuntu and find they cannot install it.

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  • Unable to boot from LiveCD/USB and even Super Grub Disk!

    - by Reuben L.
    Hi all, I'm in a fix. Basically this morning, I decided to format my Win7 as it was getting really slow and I did so with no problems. I also have a Linux Mint OS on dual boot. Since I was springcleaning my windows partition, I decided it was a good idea to do the same to my linux partition. I downloaded the latest version of Linux Mint (Julia) and burned the LiveCD. Now here is where the problem lies, when I restarted Windows and chose to boot from the LiveCD, it didn't work. No joke. There was just a little underscore blinking for a long time before it went back to GRUB which prompted me to select an OS to boot. However, when I went into my old Linux Mint OS and restarted the machine, the LiveCD worked... to a certain extent. It would load and look as though it was ready to install Linux Mint 10 but the moment it got to the option screen, the whole screen turned into a checkered and jumbled mess. At this point I thought it was the LiveCD or the .iso file. I had an Ubuntu LiveUSB for recovery purposes and I tried that. The exact same thing happened. Can't boot the LiveUSB if I restarted from Windows, but works when I reboot from Linux. BUT still the same checkered screen that doesnt respond. Did a bit of googling and reckoned it might be something wrong with my GRUB. Did some updating and didnt make a difference. Then I tried the Super Grub Disk and STUPIDLY uninstalled GRUB. (Note that booting to SGD had the exact same problem - can't be done if I rebooted from Windows). Now I can't access my Linux Mint 9 cos the the bootup screen (mbr) only has Windows 7 as an option. Remember me mentioning that I can't boot from any CD/USB/recovery CD when I reboot from Windows? And now that I can't access Linux, there's no way for me to do any form of recovery! I've tried using the command prompt utility at startup recovery but to no avail. Anyone can help me with this?

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  • Can't install any Linux distro

    - by rstreeter78
    I have been trying to install Ubuntu on my step-son's netbook and I checked and his hard disk seems to be failing and i keep getting an error message that Ubuntu is unable to install due to hard disk failure. I was wondering how and if it is possible to install Ubuntu on this hard disk without it giving me an error message. I have tried the alternate install disk image and the regular desktop image and get basically the same error message. Is there a way to somehow override this and get it installed

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  • Windows 7 booting and startup repair issues

    - by aardvark
    I have a MSI FR720 laptop with Windows 7 and Lubuntu partions. For quite a while (6 months or so) I've been having issues booting from my hard drive, it'd take me between 5 minutes and several hours for me to be able to have it recognize the hard drive as a bootable device. I did several disk checks on it, and my hard drive seems in perfect condition, and the fact that booting would usually only work after removing the hard drive and trying to reset it in its slot or lightly shaking it makes me think it had something to do with the connection in the hard drive slot as opposed to the hard drive itself. I was having particular issues with it detecting the hard drive today so I decided to try booting it from an external hard drive dock. It detected it first try and so far has had no problems finding the bootable partitions on my hard drive. When I selected my Windows 7 partition from the boot menu it said that it hadn't been shut down properly last time and needed startup repair. I've done this several times over the last 6 months, so this is hardly unusual. I do startup repair, it fails, and then I try to do a system restore. The system restore also failed, and it says that no files were changed. I restart and try it again. However, this time when I get to the startup repair it's not detecting a Windows OS. I tried clicking next and doing a startup repair but the repair is always failing. If I ignore the startup repair option and instead select "Launch windows normally" it will get to the windows animation, stop halfway through and then crash into a BSoD. I can't read the error on the screen because it immediately switches to back and tries to restart. This is my first time asking a question like this online, so let me know if I need to provide any extra information and I'll do my best to give it I tried using diskpart to find the list of partitions and see if one's labelled as an active partition, but it says that no disk were detected. I can run Lubuntu just fine. I can also see all of my Windows 7 files from it EDIT: The startup repair diagnosis and repair log is this: -- Number of repair attempts: 1 Session details System Disk = Windows directory = AutoChk Run = 0 Number of root causes = 1 Test Performed: Name: Check for updates Result: Completed successfully. Error code = 0x0 Time taken = 15ms Test Performed: Name: System disk test Result: Completed successfully. Error code = 0x0 Time taken = 31ms Root cause found. If a hard disk is installed, it is not responding. -- Any chance that this is a result of me doing this through an external dock through a USB drive?

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  • Currently using View, Should I use a hard table instead?

    - by 1001010101
    I am currently debating whether my table, mapping_uGroups_uProducts, which is a view formed by the following table: CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `db`.`mapping_uGroups_uProducts` AS select distinct `X`.`upID` AS `upID`,`Z`.`ugID` AS `ugID` from ((`db`.`mapping_uProducts_Products` `X` join `db`.`productsInfo` `Y` on((`X`.`pID` = `Y`.`pID`))) join `db`.`mapping_uGroups_Groups` `Z` on((`Y`.`gID` = `Z`.`gID`))); My current query is: SELECT upID FROM uProductsInfo \ JOIN fs_uProducts USING (upID) column \ JOIN mapping_uGroups_uProducts USING (upID) -- could be faster if we use hard table and index \ JOIN mapping_fs_key USING (fsKeyID) \ WHERE fsName="OVERALL" \ AND ugID=1 \ ORDER BY score DESC \ LIMIT 0,30; which is pretty slow. (for 30 results, it requires about 10 secondes). I think the reason for my query being so slow is definitely due to the fact that that particular query relies on a VIEW which has no index to speed things up. +----+-------------+----------------+--------+----------------+---------+---------+---------------------------------------+-------+---------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+----------------+--------+----------------+---------+---------+---------------------------------------+-------+---------------------------------+ | 1 | PRIMARY | mapping_fs_key | const | PRIMARY,fsName | fsName | 386 | const | 1 | Using temporary; Using filesort | | 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 19706 | Using where | | 1 | PRIMARY | uProductsInfo | eq_ref | PRIMARY | PRIMARY | 4 | mapping_uGroups_uProducts.upID | 1 | Using index | | 1 | PRIMARY | fs_uProducts | ref | upID | upID | 4 | db.uProductsInfo.upID | 221 | Using where | | 2 | DERIVED | X | ALL | PRIMARY | NULL | NULL | NULL | 40772 | Using temporary | | 2 | DERIVED | Y | eq_ref | PRIMARY | PRIMARY | 4 | db.X.pID | 1 | Distinct | | 2 | DERIVED | Z | ref | PRIMARY | PRIMARY | 4 | db.Y.gID | 2 | Using index; Distinct | +----+-------------+----------------+--------+----------------+---------+---------+---------------------------------------+-------+---------------------------------+ 7 rows in set (0.48 sec) The explain here looks pretty cryptic, and I don't know whether I should drop view and write a script to just insert everything in the view to a hard table. ( obviously, it will lose the flexibility of the view since the mapping changes quite frequently). Does anyone have any idea to how I can optimize my schema better?

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  • What is the proper way of hard-coding sections in a UITableView?

    - by Sheehan Alam
    I have a UITableView with 3 sections that are hard coded. Everything is working fine, but I am not sure if I am doing it correctly. Define number of rows in section: - (NSInteger)tableView:(UITableView *)tblView numberOfRowsInSection:(NSInteger)section { NSInteger rows; //Bio Section if(section == 0){ rows = 2; } //Profile section else if(section == 1){ rows = 5; } //Count section else if(section == 2){ rows = 3; } } return rows; } Here is where I build my cells: - (UITableViewCell *)tableView:(UITableView *)tblView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [tblView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier] autorelease]; } cell.textLabel.numberOfLines = 5; cell.textLabel.font = [UIFont fontWithName:@"Helvetica" size:(10.0)]; cell.textLabel.lineBreakMode = UILineBreakModeWordWrap; if ([self.message_source isEqualToString:@"default"]) { if (indexPath.section == 0) { if (indexPath.row == 0) { cell.textLabel.text = [Utils formatMessage:[NSString stringWithFormat: @"%@", mySTUser.bio]]; cell.detailTextLabel.text = nil; } else if(indexPath.row == 1){ cell.textLabel.text = [NSString stringWithFormat: @"%@", mySTUser.website]; cell.detailTextLabel.text = nil; cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator; } } } //more code exists, but you get the point... Now I define my number of sections - (NSInteger)numberOfSectionsInTableView:(UITableView *)tblView { return 3; } Is this the proper way of hard-coding my UITableView? Will I run into any issues when cells are reused?

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  • How do you re-mount an ext3 fs readwrite after it gets mounted readonly from a disk error?

    - by cagenut
    Its a relatively common problem when something goes wrong in a SAN for ext3 to detect the disk write errors and remount the filesystem read-only. Thats all well and good, only when the SAN is fixed I can't figure out how to re-re-mount the filesystem read-write without rebooting. Behold: [root@localhost ~]# multipath -ll mpath0 (36001f93000a310000299000200000000) dm-2 XIOTECH,ISE1400 [size=1.1T][features=1 queue_if_no_path][hwhandler=0][rw] \_ round-robin 0 [prio=2][active] \_ 1:0:0:1 sdb 8:16 [active][ready] \_ 2:0:0:1 sdc 8:32 [active][ready] [root@localhost ~]# mount /dev/mapper/mpath0 /mnt/foo [root@localhost ~]# touch /mnt/foo/blah All good, now I yank the LUN out from under it. [root@localhost ~]# touch /mnt/foo/blah [root@localhost ~]# touch /mnt/foo/blah touch: cannot touch `/mnt/foo/blah': Read-only file system [root@localhost ~]# tail /var/log/messages Mar 18 13:17:33 localhost multipathd: sdb: tur checker reports path is down Mar 18 13:17:34 localhost multipathd: sdc: tur checker reports path is down Mar 18 13:17:35 localhost kernel: Aborting journal on device dm-2. Mar 18 13:17:35 localhost kernel: Buffer I/O error on device dm-2, logical block 1545 Mar 18 13:17:35 localhost kernel: lost page write due to I/O error on dm-2 Mar 18 13:17:36 localhost kernel: ext3_abort called. Mar 18 13:17:36 localhost kernel: EXT3-fs error (device dm-2): ext3_journal_start_sb: Detected aborted journal Mar 18 13:17:36 localhost kernel: Remounting filesystem read-only It only thinks its read-only, in reality its not even there. [root@localhost ~]# multipath -ll sdb: checker msg is "tur checker reports path is down" sdc: checker msg is "tur checker reports path is down" mpath0 (36001f93000a310000299000200000000) dm-2 XIOTECH,ISE1400 [size=1.1T][features=0][hwhandler=0][rw] \_ round-robin 0 [prio=0][enabled] \_ 1:0:0:1 sdb 8:16 [failed][faulty] \_ 2:0:0:1 sdc 8:32 [failed][faulty] [root@localhost ~]# ll /mnt/foo/ ls: reading directory /mnt/foo/: Input/output error total 20 -rw-r--r-- 1 root root 0 Mar 18 13:11 bar How it still remembers that 'bar' file being there... mystery, but not important right now. Now I re-present the LUN: [root@localhost ~]# tail /var/log/messages Mar 18 13:23:58 localhost multipathd: sdb: tur checker reports path is up Mar 18 13:23:58 localhost multipathd: 8:16: reinstated Mar 18 13:23:58 localhost multipathd: mpath0: queue_if_no_path enabled Mar 18 13:23:58 localhost multipathd: mpath0: Recovered to normal mode Mar 18 13:23:58 localhost multipathd: mpath0: remaining active paths: 1 Mar 18 13:23:58 localhost multipathd: dm-2: add map (uevent) Mar 18 13:23:58 localhost multipathd: dm-2: devmap already registered Mar 18 13:23:59 localhost multipathd: sdc: tur checker reports path is up Mar 18 13:23:59 localhost multipathd: 8:32: reinstated Mar 18 13:23:59 localhost multipathd: mpath0: remaining active paths: 2 Mar 18 13:23:59 localhost multipathd: dm-2: add map (uevent) Mar 18 13:23:59 localhost multipathd: dm-2: devmap already registered [root@localhost ~]# multipath -ll mpath0 (36001f93000a310000299000200000000) dm-2 XIOTECH,ISE1400 [size=1.1T][features=1 queue_if_no_path][hwhandler=0][rw] \_ round-robin 0 [prio=2][enabled] \_ 1:0:0:1 sdb 8:16 [active][ready] \_ 2:0:0:1 sdc 8:32 [active][ready] Great right? It says [rw] right there. Not so fast: [root@localhost ~]# touch /mnt/foo/blah touch: cannot touch `/mnt/foo/blah': Read-only file system OK, doesn't do it automatically, I'll just give it a little push: [root@localhost ~]# mount -o remount /mnt/foo mount: block device /dev/mapper/mpath0 is write-protected, mounting read-only Noooooooooo. I have tried all sorts of different mount/tune2fs/dmsetup commands and I cannot figure out how to get it to un-flag the block device as write-protected. Rebooting will fix it, but I'd much rather do it on-line. An hour of googling has gotten me nowhere either. Save me ServerFault.

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  • Clarification On Write-Caching Policy, Its Underlying Options And How It Applies To Hard Drives And Solid-State Drives

    - by Boris_yo
    In last week after doing more research on subject matter, I have been wondering about what I have been neglecting all those years to understand write-caching policy, always leaving it on default setting. Write-caching policy improves writing performance and consists of write-back caching and write-cache buffer flushing. This is how I understand all the above, but correct me if I erred somewhere: Write-through cache / Write-through caching itself is not a part of write caching policy per se and it's when data is written to both cache and storage device so if Windows will need that data later again, it is retrieved from cache and not from storage device which means only improved read performance as there is no need for waiting for storage device to read required data again. Since data is still written to storage device, write performance isn't improved and represents no risk of data loss or corruption in case of power failure or system crash while only data in cache gets lost. This option seems to be enabled by default and is recommended for removable devices with no need to use function of "Safely Remove Hardware" on user's part. Write-back caching is similar to above but without writing data to storage device, periodically releasing data from cache and writing to storage device when it is idle. In my opinion this option improves both read and write performance but represents risk if power failure or system crash occurs with the outcome of not only losing data eventually to be written to storage device, but causing file inconsistencies or corrupted file system. Write-back caching cannot be enabled together with write-through caching and it is not recommended to be enabled if no backup power supply is availabe. Write-cache buffer flushing I reckon is similar to write-back caching but enables immediate release and writing of data from cache to storage device right before power outage occurs but I don't know if it applies also to occasional system crash. This option seem to be complementary to write-back cache reducing or potentially eliminating risk of data loss or corruption of file system. I have questions about relevance of last 2 options to today's modern SSDs in order to get best performance and with less wear on SSDs: I know that traditional hard drives come with onboard cache (I wonder what type of cache that is), but do SSDs also come with cache? Assuming they do, is this cache faster than their NAND flash and system RAM and worth taking the risk of utilizing it by enabling write-back cache? I read somewhere that generally storage device's cache is faster than RAM, but I want to be sure. Additionally I read that write-caching should be enabled since current data that is to be written later to NAND flash is kept for a while in cache and provided there is data that gets modified a lot before finally being written, holding of this data and its periodic release reduces its write times to SSD thereby reducing its wearing. Now regarding to write-cache buffer flushing, I heard that SSD controllers are so fast by themselves that enabling this option is not required, because they manage flushing. However, once again, I don't know if SSDs have their own onboard cache and whether or not it is faster than their NAND flash and system RAM because if it is, keeping this option enabled would make sense. Recently I have posted question about issue with my Intel 330 SSD 120GB which was main reason to do deeper research having suspicion of write-caching policy being the culprit of SSD's freezing issue assuming data being released is what causes freezes. Currently I have write-cache enabled and write-cache buffer flushing disabled because I believe SSD controller's management of write-cache flushing and Windows write-cache buffer flushing are conflicting with each other: Since I want to troubleshoot in small steps to finally determine the source of issue, I have decided to start with write-caching policy and the move to drivers, switching to AHCI later on and finally disabling DIPM (device initiated power management) through registry modification thanks to @TomWijsman

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  • How do you re-mount an ext3 fs readwrite after it gets mounted readonly from a disk error?

    - by cagenut
    Its a relatively common problem when something goes wrong in a SAN for ext3 to detect the disk write errors and remount the filesystem read-only. Thats all well and good, only when the SAN is fixed I can't figure out how to re-re-mount the filesystem read-write without rebooting. Behold: [root@localhost ~]# multipath -ll mpath0 (36001f93000a310000299000200000000) dm-2 XIOTECH,ISE1400 [size=1.1T][features=1 queue_if_no_path][hwhandler=0][rw] \_ round-robin 0 [prio=2][active] \_ 1:0:0:1 sdb 8:16 [active][ready] \_ 2:0:0:1 sdc 8:32 [active][ready] [root@localhost ~]# mount /dev/mapper/mpath0 /mnt/foo [root@localhost ~]# touch /mnt/foo/blah All good, now I yank the LUN out from under it. [root@localhost ~]# touch /mnt/foo/blah [root@localhost ~]# touch /mnt/foo/blah touch: cannot touch `/mnt/foo/blah': Read-only file system [root@localhost ~]# tail /var/log/messages Mar 18 13:17:33 localhost multipathd: sdb: tur checker reports path is down Mar 18 13:17:34 localhost multipathd: sdc: tur checker reports path is down Mar 18 13:17:35 localhost kernel: Aborting journal on device dm-2. Mar 18 13:17:35 localhost kernel: Buffer I/O error on device dm-2, logical block 1545 Mar 18 13:17:35 localhost kernel: lost page write due to I/O error on dm-2 Mar 18 13:17:36 localhost kernel: ext3_abort called. Mar 18 13:17:36 localhost kernel: EXT3-fs error (device dm-2): ext3_journal_start_sb: Detected aborted journal Mar 18 13:17:36 localhost kernel: Remounting filesystem read-only It only thinks its read-only, in reality its not even there. [root@localhost ~]# multipath -ll sdb: checker msg is "tur checker reports path is down" sdc: checker msg is "tur checker reports path is down" mpath0 (36001f93000a310000299000200000000) dm-2 XIOTECH,ISE1400 [size=1.1T][features=0][hwhandler=0][rw] \_ round-robin 0 [prio=0][enabled] \_ 1:0:0:1 sdb 8:16 [failed][faulty] \_ 2:0:0:1 sdc 8:32 [failed][faulty] [root@localhost ~]# ll /mnt/foo/ ls: reading directory /mnt/foo/: Input/output error total 20 -rw-r--r-- 1 root root 0 Mar 18 13:11 bar How it still remembers that 'bar' file being there... mystery, but not important right now. Now I re-present the LUN: [root@localhost ~]# tail /var/log/messages Mar 18 13:23:58 localhost multipathd: sdb: tur checker reports path is up Mar 18 13:23:58 localhost multipathd: 8:16: reinstated Mar 18 13:23:58 localhost multipathd: mpath0: queue_if_no_path enabled Mar 18 13:23:58 localhost multipathd: mpath0: Recovered to normal mode Mar 18 13:23:58 localhost multipathd: mpath0: remaining active paths: 1 Mar 18 13:23:58 localhost multipathd: dm-2: add map (uevent) Mar 18 13:23:58 localhost multipathd: dm-2: devmap already registered Mar 18 13:23:59 localhost multipathd: sdc: tur checker reports path is up Mar 18 13:23:59 localhost multipathd: 8:32: reinstated Mar 18 13:23:59 localhost multipathd: mpath0: remaining active paths: 2 Mar 18 13:23:59 localhost multipathd: dm-2: add map (uevent) Mar 18 13:23:59 localhost multipathd: dm-2: devmap already registered [root@localhost ~]# multipath -ll mpath0 (36001f93000a310000299000200000000) dm-2 XIOTECH,ISE1400 [size=1.1T][features=1 queue_if_no_path][hwhandler=0][rw] \_ round-robin 0 [prio=2][enabled] \_ 1:0:0:1 sdb 8:16 [active][ready] \_ 2:0:0:1 sdc 8:32 [active][ready] Great right? It says [rw] right there. Not so fast: [root@localhost ~]# touch /mnt/foo/blah touch: cannot touch `/mnt/foo/blah': Read-only file system OK, doesn't do it automatically, I'll just give it a little push: [root@localhost ~]# mount -o remount /mnt/foo mount: block device /dev/mapper/mpath0 is write-protected, mounting read-only The hell you are: [root@localhost ~]# mount -o remount,rw /mnt/foo mount: block device /dev/mapper/mpath0 is write-protected, mounting read-only Noooooooooo. I have tried all sorts of different mount/tune2fs/dmsetup commands and I cannot figure out how to get it to un-flag the block device as write-protected. Rebooting will fix it, but I'd much rather do it on-line. An hour of googling has gotten me nowhere either. Save me ServerFault.

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  • Why Are Minimized Programs Often Slow to Open Again?

    - by Jason Fitzpatrick
    It seems particularly counterintuitive: you minimize an application because you plan on returning to it later and wish to skip shutting the application down and restarting it later, but sometimes maximizing it takes even longer than launching it fresh. What gives? Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites. The Question SuperUser reader Bart wants to know why he’s not saving any time with application minimization: I’m working in Photoshop CS6 and multiple browsers a lot. I’m not using them all at once, so sometimes some applications are minimized to taskbar for hours or days. The problem is, when I try to maximize them from the taskbar – it sometimes takes longer than starting them! Especially Photoshop feels really weird for many seconds after finally showing up, it’s slow, unresponsive and even sometimes totally freezes for minute or two. It’s not a hardware problem as it’s been like that since always on all on my PCs. Would I also notice it after upgrading my HDD to SDD and adding RAM (my main PC holds 4 GB currently)? Could guys with powerful pcs / macs tell me – does it also happen to you? I guess OSes somehow “focus” on active software and move all the resources away from the ones that run, but are not used. Is it possible to somehow set RAM / CPU / HDD priorities or something, for let’s say, Photoshop, so it won’t slow down after long period of inactivity? So what is the deal? Why does he find himself waiting to maximize a minimized app? The Answer SuperUser contributor Allquixotic explains why: Summary The immediate problem is that the programs that you have minimized are being paged out to the “page file” on your hard disk. This symptom can be improved by installing a Solid State Disk (SSD), adding more RAM to your system, reducing the number of programs you have open, or upgrading to a newer system architecture (for instance, Ivy Bridge or Haswell). Out of these options, adding more RAM is generally the most effective solution. Explanation The default behavior of Windows is to give active applications priority over inactive applications for having a spot in RAM. When there’s significant memory pressure (meaning the system doesn’t have a lot of free RAM if it were to let every program have all the RAM it wants), it starts putting minimized programs into the page file, which means it writes out their contents from RAM to disk, and then makes that area of RAM free. That free RAM helps programs you’re actively using — say, your web browser — run faster, because if they need to claim a new segment of RAM (like when you open a new tab), they can do so. This “free” RAM is also used as page cache, which means that when active programs attempt to read data on your hard disk, that data might be cached in RAM, which prevents your hard disk from being accessed to get that data. By using the majority of your RAM for page cache, and swapping out unused programs to disk, Windows is trying to improve responsiveness of the program(s) you are actively using, by making RAM available to them, and caching the files they access in RAM instead of the hard disk. The downside of this behavior is that minimized programs can take a while to have their contents copied from the page file, on disk, back into RAM. The time increases the larger the program’s footprint in memory. This is why you experience that delay when maximizing Photoshop. RAM is many times faster than a hard disk (depending on the specific hardware, it can be up to several orders of magnitude). An SSD is considerably faster than a hard disk, but it is still slower than RAM by orders of magnitude. Having your page file on an SSD will help, but it will also wear out the SSD more quickly than usual if your page file is heavily utilized due to RAM pressure. Remedies Here is an explanation of the available remedies, and their general effectiveness: Installing more RAM: This is the recommended path. If your system does not support more RAM than you already have installed, you will need to upgrade more of your system: possibly your motherboard, CPU, chassis, power supply, etc. depending on how old it is. If it’s a laptop, chances are you’ll have to buy an entire new laptop that supports more installed RAM. When you install more RAM, you reduce memory pressure, which reduces use of the page file, which is a good thing all around. You also make available more RAM for page cache, which will make all programs that access the hard disk run faster. As of Q4 2013, my personal recommendation is that you have at least 8 GB of RAM for a desktop or laptop whose purpose is anything more complex than web browsing and email. That means photo editing, video editing/viewing, playing computer games, audio editing or recording, programming / development, etc. all should have at least 8 GB of RAM, if not more. Run fewer programs at a time: This will only work if the programs you are running do not use a lot of memory on their own. Unfortunately, Adobe Creative Suite products such as Photoshop CS6 are known for using an enormous amount of memory. This also limits your multitasking ability. It’s a temporary, free remedy, but it can be an inconvenience to close down your web browser or Word every time you start Photoshop, for instance. This also wouldn’t stop Photoshop from being swapped when minimizing it, so it really isn’t a very effective solution. It only helps in some specific situations. Install an SSD: If your page file is on an SSD, the SSD’s improved speed compared to a hard disk will result in generally improved performance when the page file has to be read from or written to. Be aware that SSDs are not designed to withstand a very frequent and constant random stream of writes; they can only be written over a limited number of times before they start to break down. Heavy use of a page file is not a particularly good workload for an SSD. You should install an SSD in combination with a large amount of RAM if you want maximum performance while preserving the longevity of the SSD. Use a newer system architecture: Depending on the age of your system, you may be using an out of date system architecture. The “system architecture” is generally defined as the “generation” (think generations like children, parents, grandparents, etc.) of the motherboard and CPU. Newer generations generally support faster I/O (input/output), better memory bandwidth, lower latency, and less contention over shared resources, instead providing dedicated links between components. For example, starting with the “Nehalem” generation (around 2009), the Front-Side Bus (FSB) was eliminated, which removed a common bottleneck, because almost all system components had to share the same FSB for transmitting data. This was replaced with a “point to point” architecture, meaning that each component gets its own dedicated “lane” to the CPU, which continues to be improved every few years with new generations. You will generally see a more significant improvement in overall system performance depending on the “gap” between your computer’s architecture and the latest one available. For example, a Pentium 4 architecture from 2004 is going to see a much more significant improvement upgrading to “Haswell” (the latest as of Q4 2013) than a “Sandy Bridge” architecture from ~2010. Links Related questions: How to reduce disk thrashing (paging)? Windows Swap (Page File): Enable or Disable? Also, just in case you’re considering it, you really shouldn’t disable the page file, as this will only make matters worse; see here. And, in case you needed extra convincing to leave the Windows Page File alone, see here and here. Have something to add to the explanation? Sound off in the the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.     

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  • I need to write a program that reads angles in radians from an input disk and converts them in degre

    - by Amadou
    Write a program that reads angles in radians from an input disk le and converts them into degrees, minutes, and seconds. Output should be written into another le. A sample input le could be: # this is a comment # your program should be able to skip comment lines # and blank lines # input radian numbers could be seperated by blanks 0.0 1.0 # or by a newline 3.141593 6.0

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  • Is it possible to gzip and upload this string to Amazon S3 without ever being written to disk?

    - by BigJoe714
    I know this is probably possible using Streams, but I wasn't sure the correct syntax. I would like to pass a string to the Save method and have it gzip the string and upload it to Amazon S3 without ever being written to disk. The current method inefficiently reads/writes to disk in between. The S3 PutObjectRequest has a constructor with InputStream input as an option. import java.io.*; import java.util.zip.GZIPOutputStream; import com.amazonaws.auth.PropertiesCredentials; import com.amazonaws.services.s3.AmazonS3; import com.amazonaws.services.s3.AmazonS3Client; import com.amazonaws.services.s3.model.PutObjectRequest; public class FileStore { public static void Save(String data) throws IOException { File file = File.createTempFile("filemaster-", ".htm"); file.deleteOnExit(); Writer writer = new OutputStreamWriter(new FileOutputStream(file)); writer.write(data); writer.flush(); writer.close(); String zippedFilename = gzipFile(file.getAbsolutePath()); File zippedFile = new File(zippedFilename); zippedFile.deleteOnExit(); AmazonS3 s3 = new AmazonS3Client(new PropertiesCredentials( new FileInputStream("AwsCredentials.properties"))); String bucketName = "mybucket"; String key = "test/" + zippedFile.getName(); s3.putObject(new PutObjectRequest(bucketName, key, zippedFile)); } public static String gzipFile(String filename) throws IOException { try { // Create the GZIP output stream String outFilename = filename + ".gz"; GZIPOutputStream out = new GZIPOutputStream(new FileOutputStream(outFilename)); // Open the input file FileInputStream in = new FileInputStream(filename); // Transfer bytes from the input file to the GZIP output stream byte[] buf = new byte[1024]; int len; while ((len = in.read(buf)) > 0) { out.write(buf, 0, len); } in.close(); // Complete the GZIP file out.finish(); out.close(); return outFilename; } catch (IOException e) { throw e; } } }

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  • Android ListView clears when hard BACK key is pressed.

    - by Rpond
    In my android app I have a Tabhost with a ListView as one of the tabs. By clicking on an item in the ListView (an address) I start an Intent to Google Maps for directions and the choice dialog pops up for google maps, web browser etc. Problem is if I press the hard back button then the launch dialog goes away but also the ListView is cleared. Any idea why?

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  • ASP.NET Performance, 100 "Memory Hard Faults" indiciate a memory swapping problem?

    - by Robert
    With a customer web site we currently experiences performance problems. While analyzing the problem we found an unexpected amount of of 112 "Memory Hard Faults" per minute. Does anybody can interpret the meaning of this value? Does this happen, when memory swapping is necessary - so the root cause is not sufficient memory? Even if the CPU value seems high, it is not the main problem for the slow web site. Do you agree?

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