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• Installed Ubuntu on 12.04 on my MacBook Air now I want to expand the partition

  - by Josh

  I recently installed Ubuntu 12.04 on a 40GB partition on my Mac Book Air (5,2). I'm having so much fun with it, I'm ready to make the switch permanently and replace it as the primary OS on my machine. I realize I can wipe the machine and start from scratch, but I'm looking for alternatives since I like my current setup. Options are... Create a backup and restore the back up to a larger partition (Assuming I should keep the default OS X install for firmware updates) Create a backup and restore to the entire drive (create a restore usb stick for OSX - not sure if that's possible?) re-size my current partition and wipe the OS X partition and either, A. re-install OS X (similar to option 1) or B. create the USB key (similar to option 2). Thoughts? Any other suggestions? Would also like thoughts on the "optimal" or "best practice" for partitioning Ubuntu. Thanks!

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• Resize hard drive partition to make more space for /var

  - by user3357381

  I am running out of space in the /var partition. I have plenty of space in my /home partition. How do I shrink the /home partition to make more space for the /var partition? I have read some blogs that say to use the GParted Live CD. As a new user, I'm not quite sure if this is the ideal route. What is the best way to create more space for /var ? Output of df -h : Filesystem Size Used Avail Use% Mounted on /dev/sda2 19G 7.1G 11G 41% / none 4.0K 0 4.0K 0% /sys/fs/cgroup udev 7.9G 8.0K 7.9G 1% /dev tmpfs 1.6G 1.5M 1.6G 1% /run none 5.0M 0 5.0M 0% /run/lock none 7.9G 624K 7.9G 1% /run/shm none 100M 60K 100M 1% /run/user /dev/sda4 454M 75M 352M 18% /boot /dev/sda5 2.3G 2.1G 36M 99% /var /dev/sda3 178G 1.3G 168G 1% /home /dev/sda6 2.8G 5.8M 2.6G 1% /tmp /dev/sdb1 3.7T 401G 3.3T 11% /hdd

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• Ubuntu partition won't display on screen

  - by Danny

  I installed ggobi on my MacBook Pro, and it wasn't working right. I looked up some information, and found this site: Gtk Warning: Cannot open display I followed the vague instructions, but I think I just typed export DISPLAY=:0 directly into my terminal (I'm still in my Mac partition at this point). Fast forward a few days, and I try to go into my Ubuntu partition. It only gives me command line options. I remember my reckless input from a few days back, and I'm certain that it is the issue. My problem is that I have no idea how to get my previous display settings back. My Mac partition seems unaffected, but it'd be nice to get back into my Ubuntu partition. My last resort is completely reverting my computer to my most recent backup before I changed it, but if anyone out there knows how to fix this, I'd greatly appreciate it. Thanks in advance.

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• installer can't find partition, but fdisk can find them

  - by pxd

  I'm installing ubuntu 12.04, my system had install 2 system -- winxp and ubuntu 10.10. Now, I want to update ubuntu to 12.04. I use usb disk to install 12.04. But, the installer can't not find my partition in my harddisk. But, the fdisk can find them. Can you help me? How to do? ubuntu@ubuntu:~$ sudo lshw -short H/W path Device Class Description system HP 2230s (NN868PA#AB2) /0 bus 3037 /0/9 memory 64KiB BIOS /0/0 processor Intel(R) Core(TM)2 Duo CPU T6570 @ 2.10GHz /0/0/1 memory 2MiB L2 cache /0/0/3 memory 32KiB L1 cache /0/0/0.1 processor Logical CPU /0/0/0.2 processor Logical CPU /0/2 memory 32KiB L1 cache /0/4 memory 2GiB System Memory /0/4/0 memory SODIMM [empty] /0/4/1 memory 2GiB SODIMM DDR2 Synchronous 800 MHz (1.2 ns) /0/100 bridge Mobile 4 Series Chipset Memory Controller Hub /0/100/2 display Mobile 4 Series Chipset Integrated Graphics Controller /0/100/2.1 display Mobile 4 Series Chipset Integrated Graphics Controller /0/100/1a bus 82801I (ICH9 Family) USB UHCI Controller #4 /0/100/1a.1 bus 82801I (ICH9 Family) USB UHCI Controller #5 /0/100/1a.2 bus 82801I (ICH9 Family) USB UHCI Controller #6 /0/100/1a.7 bus 82801I (ICH9 Family) USB2 EHCI Controller #2 /0/100/1b multimedia 82801I (ICH9 Family) HD Audio Controller /0/100/1c bridge 82801I (ICH9 Family) PCI Express Port 1 /0/100/1c.1 bridge 82801I (ICH9 Family) PCI Express Port 2 /0/100/1c.1/0 wlan1 network PRO/Wireless 5100 AGN [Shiloh] Network Connection /0/100/1c.2 bridge 82801I (ICH9 Family) PCI Express Port 3 /0/100/1c.4 bridge 82801I (ICH9 Family) PCI Express Port 5 /0/100/1c.5 bridge 82801I (ICH9 Family) PCI Express Port 6 /0/100/1c.5/0 eth1 network 88E8072 PCI-E Gigabit Ethernet Controller /0/100/1d bus 82801I (ICH9 Family) USB UHCI Controller #1 /0/100/1d.1 bus 82801I (ICH9 Family) USB UHCI Controller #2 /0/100/1d.2 bus 82801I (ICH9 Family) USB UHCI Controller #3 /0/100/1d.7 bus 82801I (ICH9 Family) USB2 EHCI Controller #1 /0/100/1e bridge 82801 Mobile PCI Bridge /0/100/1f bridge ICH9M LPC Interface Controller /0/100/1f.2 scsi0 storage 82801IBM/IEM (ICH9M/ICH9M-E) 4 port SATA Controller [AHCI mode] /0/100/1f.2/0 /dev/sda disk 500GB WDC WD5000BEVT-0 /0/100/1f.2/0/1 /dev/sda1 volume 48GiB Windows NTFS volume /0/100/1f.2/0/2 /dev/sda2 volume 416GiB Extended partition /0/100/1f.2/0/2/5 /dev/sda5 volume 97GiB HPFS/NTFS partition /0/100/1f.2/0/2/6 /dev/sda6 volume 198GiB HPFS/NTFS partition /0/100/1f.2/0/2/7 /dev/sda7 volume 27GiB Linux filesystem partition /0/100/1f.2/0/2/8 /dev/sda8 volume 93GiB Linux filesystem partition /0/100/1f.2/1 /dev/cdrom disk CDDVDW TS-L633M /0/1 scsi6 storage /0/1/0.0.0 /dev/sdb disk 15GB STORAGE DEVICE /0/1/0.0.0/0 /dev/sdb disk 15GB /0/1/0.0.0/0/1 /dev/sdb1 volume 14GiB Windows FAT volume /1 power HZ04037 ubuntu@ubuntu:~$ ubuntu@ubuntu:~$ sudo fdisk -l Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x31263125 Device Boot Start End Blocks Id System /dev/sda1 * 63 102277727 51138832+ 7 HPFS/NTFS/exFAT /dev/sda2 102277728 976784129 437253201 f W95 Ext'd (LBA) /dev/sda5 102277791 307078127 102400168+ 7 HPFS/NTFS/exFAT /dev/sda6 307078191 724141151 208531480+ 7 HPFS/NTFS/exFAT /dev/sda7 724142080 781459455 28658688 83 Linux /dev/sda8 781461504 976771071 97654784 83 Linux Disk /dev/sdb: 15.9 GB, 15931539456 bytes 64 heads, 32 sectors/track, 15193 cylinders, total 31116288 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x0009eb92 Device Boot Start End Blocks Id Systemfile:///home/ubuntu/Pictures/Screenshot%20from%202012-07-07%2010:25:40.png /dev/sdb1 * 32 31115263 15557616 c W95 FAT32 (LBA) ubuntu 12.04 installer can't find the partition in my hard disk, only find device - /dev/sda.(sorry, I'm new user, so can't send image.)

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• Ubuntu 13.10 Installer freezes on partition recognition on Alienware M17x

  - by Mutewinter

  I'm trying to install Ubuntu 13.10 on an Alienware M17x, after bypassing the graphical problems with "nomodeset" (annoying!), I'm facing a rather different problem: I click on "Install Ubuntu", the guided installation progress reach the point where the partition, mount point etc. needs to be selected and...nothing. In the partition selection menu it sees only dev/sda, but in the window where the actual way the disk is partitioned should appear nothing shows, it's blank. I've tried to click on "change..." to try to force it to read something, but the installer simply quits. The button "change partition table" etcetera are greyed out (well, obviously, since no partition table has been read). What's that? The Alienware has Windows 7 and legacy BIOS (so no UEFI here). Anyone has an idea? Thanks for your time and help!

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• Librated error when creating partition table

  - by Marko

  I bought a Dell Inspiron 5521 laptop a few days ago that came with Ubuntu preinstalled. I haven't used Ubuntu yet, and I don't have any experience in using it. I wanted to install Windows 7 64-bit on my laptop alongside Ubuntu, and made two bootable USB drives with Gparted and Windows 7. There wasn't a suitable partition on my laptop in which I could install Windows 7. I've read the instructions for using Gparted to create or manage my hard drive. I inserted the USB, booted from BIOS, and followed the procedure in installing Gparted. Then I entered Gparted, and the following error occurred: Librated error when Creating partition table. It asked me to click on either OK or Cancel. Either way I had my hard disk shown to me in the user window, in partitions that were made by the manufacturer: Partition File sys Label Size Flags /dev/sda1 fat32 dellutility 300.00 Mib diag /dev/sda2 fat32 os 3.00 Gib lba /dev/sda3 ext4 912.46 Gib boot /dev/sda4 extended 15.75 Gib (had a subpart) /dev/sda5 linux-swap 15.75 Gib ...and a option to switch to dev/sdb that's unused and of capacity 3Gib. I've used the biggest partition 912.46 Gib, and tried to reduce its size, and clicked OK. Then when I tried to make a new partition, it said it can't make any more partitions, no more than a maximum of 5. I would like to keep Ubuntu and slowly learn, but I also need to use programs that work in Windows. Thank you for taking the time to answer my question.

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• update-grub is setting a wrong linux root partition

  - by adrian m

  Initially, Ubuntu was installed on another partition (sda5 or sda4). At some point I did manually move the root partition to sda2. Now, the problem is that whenever a new kernel is installed, the automatic regeneration of the menu.lst is using the OLD Linux partition. So I have to manually change in menu.lst the lines : root (hd0,5) into root (hd0,1) How can I configure update-grub to automatically generate menu.lst with the current Linux root partition? I assume that the (hd0,5) was written somewhere at installation, but I couldn't find it.

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• How to I make my bootcamp partition bootable again?

  - by KJFMusic

  I'm having a similar problem as everyone else in this posting. I have 5 partitions. 3 of which I created for my Mac OS Lion installation, Windows 7 installation and a 3rd for storage. Everything was running fine for quite sometime until recently. My Windows 7 installation has suddenly stopped booting. Instead of a start up screen I get: Windows failed to start. A recent hardware or software change might be the cause. File: \BOOT\BCD Status: 0xc000000d Info: An error occurred while attempting to read the boot configuration data Mac OS Lion starts up fine. I'm unable to mount my "Bootcamp" partition nor the "Storage" partition. On top of that "Storage" has been renamed to "disk0s5". When I installed Windows 7 it didn't recognize the "Storage" partition that was created in Lion so it merged what it thought was free diskspace (I'm assuming the same space that Mac OS recognized as Storage) to the Root Drive of Windows 7 (Bootcamp). Are you able to assist?

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• How to resize(increase) a root+home cloned partition from a smaller hdd?

  - by saulo

  Here is my story: I had a hd failing so I cloned it with dd to larger 500gb hd. It seemed to have worked well, but I have all this unallocated free space at the end of the disk (230gb). I tried to used gparted from a liveUSB to allocate all this space to my root+home partition (other than that I only have a small extended partition with the swap). It won't let me do this. I can only create another partition, or allocate the free space to the extend partition. I can however reduce the size of the root+home partition since I wasn't using all the space Is there a way to put this free space to my root+home partition after all? Or do I have to go with another partition. If so I'd like to separate my home from the root, reduce the root partition and create a ext4 logical home partition. What would be the best safest way to do this? Thanks so much in advance, aloha

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• How to recover my invisible HD again?

  - by pattulus

  I made this several times now, but this time something bad happened. What I did: I installed Windows 7 at a 32GB partition on my slot 2 HD in my MacPro. Windows 7 made a 105MB partition… I knew this before, but what I didn’t know was that this partition is now on my slot 4 HD. My home folder, my private videos and some other stuff are on this 1TB drive. What I found out so far: I’m currently logged in as another admin since my OS partition as well as the two other HD's aren't harmed. Disk Utility: … only shows the 105MB NTSF partition on this 1TB volume. It isn’t showing my old 1TB partition/ex-HD named "storehouse". Only the partition tab is telling me that there now is a 1TB empty free unpartitioned space. Data Rescue II: … is showing the Volume as it used to be with it's old Name "storehouse". A quick scan and a thorough scan both were done in 1 second which leds me to the conclusion that there's isn’t something deleted at all (» hope!). Data Rescue doesn’t even mention the damn "system reserved" partition. Drive Genius: … also shows the old partition and doesn’t mention the new one. But looking at the info it tells me under "content": FDisk_partition_scheme (instead of Apple_partition_scheme). Well D'oh…. Tech Tools: … doesn’t show the volume, otherwise I'd might have been tempted to press rebuild/repair. What to do next?? I think the best approach is to buy another 1TB HD and let Disk Warrior Clone my old one to it… just to be on the safe side. But what is the best thing to do after this… ???

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• Fixing damaged partition table

  - by dr4cul4

  This is continuation of Recover Extended Partition , but this time I have different problem related partition table it self. I managed to restore partition that I needed and backed up files that were crucial to me (at least those that I had space to store somewhere) OK now get to the problem. My partition table is corrupted, booting RIP Linux I can mount it in truecrypt (and other ones that recovered), but that's basically it. When I launch GParted I have unallocated drive. GParted Dev info: Device Information Model: ATA ST2000DL003-9VT1 Size: 1.82TiB Path: /dev/sda Partition table: unrecognized Heads: 255 Sectors/track: 63 Cylinders: 243201 Total Sectors: 3907029168 Sector size: 512 When I check information on unallocated space I get: File system: unallocated Size: 1.82TiB First sector: 0 Last sector: 3907029167 Total sectors: 3907029168 Warning: Can't have a partition outside the disk! Now the output of testdisc (Analyze): TestDisk 6.13, Data Recovery Utility, November 2011 Christophe GRENIER <[email protected]> http://www.cgsecurity.org Disk /dev/sda - 2000 GB / 1863 GiB - CHS 243201 255 63 Current partition structure: Partition Start End Size in sectors > 1 P Linux 13132 242 39 16353 233 8 51744768 2 E extended LBA 16807 223 1 243201 254 63 3637021626 No partition is bootable 5 L Linux 16807 223 57 20430 39 25 58191872 X extended 20430 70 1 243201 78 13 3578816632 Invalid NTFS or EXFAT boot 6 L HPFS - NTFS 20430 71 58 243201 78 13 3578816512 6 LNext Now fdisk: # fdisk -l /dev/sda Disk /dev/sda: 2000.4 GB, 2000398934016 bytes 255 heads, 63 sectors/track, 243201 cylinders, total 3907029168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00039cd0 Device Boot Start End Blocks Id System /dev/sda1 210980864 262725631 25872384 83 Linux /dev/sda2 270018504 3907040129 1818510813 f W95 Ext'd (LBA) /dev/sda5 270018560 328210431 29095936 83 Linux /dev/sda6 328212480 3907028991 1789408256 7 HPFS/NTFS/exFAT Now I would like to fix that to arrange partitions correctly, but I have no idea which tool is capable of fixing that (tried, a few, some of them offered fixing, but it was to risky at the moment - still backing up data).

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• Multi-partition USB stick

  - by nightcracker

  In my freelance job as "the dude that fixes your computer" I have an extremely handy tool, a bootable USB stick with Ubuntu LiveCD that allows me to recover and investigate in a known, working environment. Now, I want to reformat this USB stick and reinstall with Casper-RW persistance. I did this a few times before with a FAT-formatted USB stick. It was a horror. The USB drive corrupted constantly, by people accidently removing the USB stick, the computer not properly shutting down, ETC. Now what I want to create a multi-partition USB stick so I can put Ubuntu on a ext partition, but still be able to store some Windows stuff in it, by having a secondary FAT partition. However I read somewhere that Windows will only check the first partition on USB sticks, giving a problem with the first bootable linux partition. Is this possible on some way? EDIT Perhaps it wasn't clear what the problem is. The problem is that I read somewhere that Windows will only recognize the first partition on a USB stick. But I want two partitions, a ext partition and a FAT partition. No issues so far, but in order to be bootable the ext partition must be the first one!

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• Can I delete EFI System Partition without harming other data on drive?

  - by Andy

  I have three external HDD's in a USB enclosure. After a recent upgrade to Win7, during which these three drives were actually installed inside the PC tower, two of the three drives now have a 200MB EFI partition, and the two drives do not show up as usable drives under either Win7 or Snow Leopard. One of the drives is empty; the other one, however, has a bunch of stuff on it that I want to save if possible. My question is, how can I get back to this data? Can I simply delete the EFI partition, and all will be well? Or do I have to do something trickier? Or am I just hosed?

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• Is it possible to convert an ntfs partition to ext3?

  - by Johnny

  Is it possible to convert an ntfs partition to ext3?

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• Partition and mount my secondary hard drive on CentOS 5.5 64bit?

  - by Andrew Fashion

  I am trying to prepare my second hard drive for user image uploads. Here is the current layout: # sudo parted /dev/sda print Model: ATA WDC WD2500KS-00M (scsi) Disk /dev/sda: 250GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 32.3kB 107MB 107MB primary ext3 boot 2 107MB 8595MB 8488MB primary linux-swap 3 8595MB 10.7GB 2147MB primary ext3 4 10.7GB 250GB 239GB extended 5 10.7GB 250GB 239GB logical ext3 Information: Don't forget to update /etc/fstab, if necessary. I am assuming #4 is my secondary drive? How do I partition and mount it so I can begin using it? And how do I add to fstab? I understand if it's to many questions in one, just help me with whatever you can I guess :) Thank you for any help!

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• Free space not reclaimed after online resizing ext4 in Ubuntu 9.10

  - by TiansHUo

  My root partition was filling up, with only 500 mbs left, I wanted to resize my root partition from 20 Gb to 40Gb So I resized my partition by using these steps: Using Gparted to resize another partition to give space for the EXT4 Using fdisk, deleting the root partition (on /dev/sda2), and creating it again using the new size resize2fs /dev/sda2 Updating grub2 But now the problem is that although I can boot in my new partition and the new partition shows it is 40Gb, but the free size was still 500mb. So I booted from a LiveCD and checked with e2fsck -p /dev/sda2, it reported clean. So I added the -f flag (force check), still, the drive is full.

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• Cannot resize OS X partition

  - by David Pearce

  I am trying to resize my existing Mac OS Extended partition on my Macbook to install Windows 7 (using steps similar to these), but when ever I go to apply the changes, I get this error: Partition failed Partition failed with the error: The partition cannot be resized. Try reducing the amount of change in the size of the partition. The total capacity of the hard drive in question is 260GB, with the entirety being taken up by the OS X boot partition. There is I am aiming to shrink that partition down to 60GB. How can I fix this problem? I have been reducing the amount of change by 10GB each attempt, but it still is not working. I assume the problem is that there is not a large amount of continuous space on the device. Is there some way to can do a manual defrag that would rectify this problem?

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• Cannot resize OS X partition

  - by joshhunt

  I am trying to resize my existing Mac OS Extended partition on my Macbook to install Windows 7 (using steps similar to these), but when ever I go to apply the changes, I get this error: Partition failed Partition failed with the error: The partition cannot be resized. Try reducing the amount of change in the size of the partition. The total capacity of the hard drive in question is 260GB, with the entirety being taken up by the OS X boot partition. There is I am aiming to shrink that partition down to 60GB. How can I fix this problem? I have been reducing the amount of change by 10GB each attempt, but it still is not working. I assume the problem is that there is not a large amount of continuous space on the device. Is there some way to can do a manual defrag that would rectify this problem?

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• Partitioning a bootable Flash drive

  - by mmc

  Is it possible to have a 2 partition Flash drive that looks like the following: A partition that is bootable to OS X (this will require a GUID partition table) A second partition formatted either FAT32 or NTFS that is readable on both OS X and various flavors of Windows I have set up a disk using Disk Utility on the Mac, and it boots fine with a second FAT32 partition... but Windows does not see it. Any flavor of Windows wants to format the entire drive. Has anyone done this, and if so, can you explain the steps you followed? EDIT: Making it bootable is no problem. I have that. I'm wondering how to make the second partition on a Flash drive visible to Windows. It's possible that the "second partition" is the problem, and I need Windows to be first, and HFS to be second. I'll try that tonight.

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• Can a virus on a windows 7 partition make its way into the OS X partition?

  - by hatorade

  I have a Windows 7 partition on my MBP that I installed with Boot Camp. I have reason to believe that there was a virus on my Windows 7 partition (did some scans, got some sketchy results from Avira). I decided to just wipe the entire partition using Boot Camp Restore to reformat the old partition and add it back to my OS X partition. I'm wondering however if in the time period I had the two partitions up a virus could have jumped from the Windows 7 partition onto the OS X partition, in which case I now need to worry about a virus on my OS X installation?

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• HELP! Free space not reclaimed after online resizing ext4 in Ubuntu 9.10

  - by TiansHUo

  My root partition was filling up, with only 500 mbs left, I wanted to resize my root partition from 20 Gb to 40Gb So I resized my partition by using these steps: Using Gparted to resize another partition to give space for the EXT4 Using fdisk, deleting the root partition (on /dev/sda2), and creating it again using the new size resize2fs /dev/sda2 Updating grub2 But now the problem is that although I can boot in my new partition and the new partition shows it is 40Gb, but the free size was still 500mb. So I booted from a LiveCD and checked with e2fsck -p /dev/sda2, it reported clean. So I added the -f flag (force check), still, the drive is full.

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• Create new partition on ssd hard (remove hibernate)

  - by Aleks

  I bought Dell Vostro 3360 notebook with Windows 7 It has 128 GB SSD hard disk, it is already has 4 partitions: Dell partition, Recovery partition, OS partition, Hibernate partition. Here is screenshot (Russian language, but I made some marks): I want to split OS partition, because I need c:\ and d:\ . Reason is that I have a lot of difficulties with administration mode on c:. So I tried to split OS partition but I already have 4 partitions. Can I remove hibernate partition without consequences? I have Hibernate disabled in settings, but I have hiberfil.sys file on c:\ If I can remove it, how can I do this, I can't do this with standard GUI disk managment tool

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• Combine OS partion with data partition on NAS4Free/FreeNAS

  - by Pak

  I recently built a NAS4Free (formerly FreeNAS) machine using a 256MB (yes, MB) USB drive for the OS. When I did the original install, I had the bright idea of making the OS partition just big enough for the OS and a then creating a second partition using the remainder of the drive to store stuff pertaining to the OS. I never really found a use for the data partition and I ended up running out of space on the OS partition, so now I'd like to combine the partitions into a single partition. Is this something that is possible to do while everything is up and running? If it comes down to it, I can take down the machine and do a fresh install of the OS using the entire space of the USB drive, but I'd like to use this as an opportunity to better familiarize myself with FreeBSD/UNIX type systems. If this is possible, will it interfere with the NAS4Free things? The data partition shows up in the web interface under the disks section. If I end up manually changing the partitions, I'd be concerned with NAS4Free getting confused by the missing partition.

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• Partition Wise Joins

  - by jean-pierre.dijcks

  Some say they are the holy grail of parallel computing and PWJ is the basis for a shared nothing system and the only join method that is available on a shared nothing system (yes this is oversimplified!). The magic in Oracle is of course that is one of many ways to join data. And yes, this is the old flexibility vs. simplicity discussion all over, so I won't go there... the point is that what you must do in a shared nothing system, you can do in Oracle with the same speed and methods. The Theory A partition wise join is a join between (for simplicity) two tables that are partitioned on the same column with the same partitioning scheme. In shared nothing this is effectively hard partitioning locating data on a specific node / storage combo. In Oracle is is logical partitioning. If you now join the two tables on that partitioned column you can break up the join in smaller joins exactly along the partitions in the data. Since they are partitioned (grouped) into the same buckets, all values required to do the join live in the equivalent bucket on either sides. No need to talk to anyone else, no need to redistribute data to anyone else... in short, the optimal join method for parallel processing of two large data sets. PWJ's in Oracle Since we do not hard partition the data across nodes in Oracle we use the Partitioning option to the database to create the buckets, then set the Degree of Parallelism (or run Auto DOP - see here) and get our PWJs. The main questions always asked are: How many partitions should I create? What should my DOP be? In a shared nothing system the answer is of course, as many partitions as there are nodes which will be your DOP. In Oracle we do want you to look at the workload and concurrency, and once you know that to understand the following rules of thumb. Within Oracle we have more ways of joining of data, so it is important to understand some of the PWJ ideas and what it means if you have an uneven distribution across processes. Assume we have a simple scenario where we partition the data on a hash key resulting in 4 hash partitions (H1 -H4). We have 2 parallel processes that have been tasked with reading these partitions (P1 - P2). The work is evenly divided assuming the partitions are the same size and we can scan this in time t1 as shown below. Now assume that we have changed the system and have a 5th partition but still have our 2 workers P1 and P2. The time it takes is actually 50% more assuming the 5th partition has the same size as the original H1 - H4 partitions. In other words to scan these 5 partitions, the time t2 it takes is not 1/5th more expensive, it is a lot more expensive and some other join plans may now start to look exciting to the optimizer. Just to post the disclaimer, it is not as simple as I state it here, but you get the idea on how much more expensive this plan may now look... Based on this little example there are a few rules of thumb to follow to get the partition wise joins. First, choose a DOP that is a factor of two (2). So always choose something like 2, 4, 8, 16, 32 and so on... Second, choose a number of partitions that is larger or equal to 2* DOP. Third, make sure the number of partitions is divisible through 2 without orphans. This is also known as an even number... Fourth, choose a stable partition count strategy, which is typically hash, which can be a sub partitioning strategy rather than the main strategy (range - hash is a popular one). Fifth, make sure you do this on the join key between the two large tables you want to join (and this should be the obvious one...). Translating this into an example: DOP = 8 (determined based on concurrency or by using Auto DOP with a cap due to concurrency) says that the number of partitions >= 16. Number of hash (sub) partitions = 32, which gives each process four partitions to work on. This number is somewhat arbitrary and depends on your data and system. In this case my main reasoning is that if you get more room on the box you can easily move the DOP for the query to 16 without repartitioning... and of course it makes for no leftovers on the table... And yes, we recommend up-to-date statistics. And before you start complaining, do read this post on a cool way to do stats in 11.

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• The Numerical ‘Magic’ of Cyclic Numbers

  - by Akemi Iwaya

  If you love crunching numbers or are just a fan of awesome number ‘tricks’ to impress your friends with, then you will definitely want to have a look at cyclic numbers. Dr Tony Padilla from the University of Nottingham shows how these awesome numbers work in Numberphile’s latest video. Cyclic Numbers – Numberphile [YouTube] Want to learn more about cyclic numbers? Then make sure to visit the Wikipedia page linked below! Cyclic number [Wikipedia]     

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