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  • Formula to calculate probability of unrecoverable read error during RAID rebuild

    - by OlafM
    I need to compare the reliability of different RAID systems with either consumer or enterprise drives. The formula to have the probability of success of a rebuild, ignoring mechanical problems, is simple: error_probability = 1 - (1-per_bit_error_rate)^bit_read and with 3 TB drives I get 38% probability to experience an URE (unrecoverable read error) for a 2+1 disks RAID5 (4.7% for enterprise drives) 21% for a RAID1 (2.4% for enterprise drives) 51% probability of error during recovery for the 3+1 RAID5 often used by users of SOHO products like Synologys. Most people don't know about this. Calculating the error for single disk tolerance is easy, my question concerns systems tolerant to multiple disks failures (RAID6/Z2, RAIDZ3 and RAID1 with multiple disks). If only the first disk is used for rebuild and the second one is read again from the beginning in case or an URE, then the error probability is the one calculated above squared (14.5% for consumer RAID5 2+1, 4.5% for consumer RAID1 1+2). However, I suppose (at least in ZFS that has full checksums!) that the second parity/available disk is read only where needed, meaning that only few sectors are needed: how many UREs can possibly happen in the first disk? not many, otherwise the error probability for single-disk tolerance systems would skyrocket even more than I calculated. If I'm correct, a second parity disk would practically lower the risk to extremely low values. Am I correct?

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  • Choice of an OS for a home ZFS NAS

    - by OlafM
    I am preparing a home NAS with an old Athlon 64 X2 3800+, 4 GB ECC RAM, Asus M2V MX motherboard, and a single 3 TB WDC Green (another one as mirror may be installed in the future). It's the cheapest solution I found that includes ECC memory and the higher energy consumption is offset by the lower (zero) cost of acquisition. The system will be used for: music storage and stream to other desktop computers; storage of the scanned dia slides (3-4k slides, 180 MB TIFF each one plus reduced quality JPEG version); stream of these photos to a local iPad 2 (maybe Plex App? not yet sure); (one additional) remote backup via rsync/ssh or ZFS send/receive. It will be controlled via remote ssh, maybe VNC, no monitor attached. Absolute requirement is a reliable ZFS solution, plus the ability to easily install packets/software/virtual machines and to update remotely (I will be the admin and I don't live near the NAS). I have mainly three options: NAS4free/FreeNAS OpenIndiana Solaris Express 11 (yeah yeah I know the license requirements, I will write a perl script on it to count it as development machine). Problems: NAS4free/FreeNAS (I tested only NAS4free) required embedded installation for remote upgrading, but full install for easy addition of software packets. Since I need at least AirVideo Server (linux/win) and Plex App (win/linux) to stream the photos and some videos to iPad (they both require virtualbox), but I cannot be there to install updates, NAS4free/FreeNAS are excluded. http://www.nas4free.org/general_information.html explains the issue: embedded can be remotely updated, full cannot. Solaris has also another advantage: Crashplan client supports Solaris and I'm already using it for other backups. I would like to leave the option open, even if I will be doing backups probably through zfs send/receive. NexentaStor was left out because zfs send/receive are not included in the free version. The question is now Solaris 11 Express over OpenIndiana. To ease the management, I will be using http://www.napp-it.org Which one would you suggest and why? I found lots of informations and it's difficult for me to decide. I think (from the napp-it manual) that Solaris has some additional options for SMB shares, but are they really needed at home? I think I won't even use ACLs, since normal unix-style permissions are enough. OpenIndiana has maybe more frequent updates (Solaris offers only security updates between releases), but again, do I need them? I don't think so. Moreover, this is a NAS that has to work and nothing else, I cannot risk having problems that require me to access the server. Isn't OpenIndiana a bit more... cutting edge (in the Solaris world)? I'm just asking, no need to focus on this for the answer :-) I would limit myself to these two options (SE11.1/OI) also because I will be making a NAS for me in the future (where high performances with Mac shares are also required) and Solaris has kernel support for AFP. I will use this server to gather experience as well. After this long question, thanks in advance! If you need additional info, let me know and I will update this post.

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  • Choice of an OS for a home ZFS NAS

    - by OlafM
    I am preparing a home NAS with an old Athlon 64 X2 3800+, 4 GB ECC RAM, Asus M2V MX motherboard, and a single 3 TB WDC Green (another one as mirror may be installed in the future). It's the cheapest solution I found that includes ECC memory and the higher energy consumption is offset by the lower (zero) cost of acquisition. The system will be used for: music storage and stream to other desktop computers; storage of the scanned dia slides (3-4k slides, 180 MB TIFF each one plus reduced quality JPEG version); stream of these photos to a local iPad 2 (maybe Plex App? not yet sure); (one additional) remote backup via rsync/ssh or ZFS send/receive. It will be controlled via remote ssh, maybe VNC, no monitor attached. Absolute requirement is a reliable ZFS solution, plus the ability to easily install packets/software/virtual machines and to update remotely (I will be the admin and I don't live near the NAS). I have mainly three options: NAS4free/FreeNAS OpenIndiana Solaris Express 11 (yeah yeah I know the license requirements, I will write a perl script on it to count it as development machine). Problems: NAS4free/FreeNAS (I tested only NAS4free) required embedded installation for remote upgrading, but full install for easy addition of software packets. Since I need at least AirVideo Server (linux/win) and Plex App (win/linux) to stream the photos and some videos to iPad (they both require virtualbox), but I cannot be there to install updates, NAS4free/FreeNAS are excluded. http://www.nas4free.org/general_information.html explains the issue: embedded can be remotely updated, full cannot. Solaris has also another advantage: Crashplan client supports Solaris and I'm already using it for other backups. I would like to leave the option open, even if I will be doing backups probably through zfs send/receive. NexentaStor was left out because zfs send/receive are not included in the free version. The question is now Solaris 11 Express over OpenIndiana. To ease the management, I will be using http://www.napp-it.org Which one would you suggest and why? I found lots of informations and it's difficult for me to decide. I think (from the napp-it manual) that Solaris has some additional options for SMB shares, but are they really needed at home? I think I won't even use ACLs, since normal unix-style permissions are enough. OpenIndiana has maybe more frequent updates (Solaris offers only security updates between releases), but again, do I need them? I don't think so. Moreover, this is a NAS that has to work and nothing else, I cannot risk having problems that require me to access the server. Isn't OpenIndiana a bit more... cutting edge (in the Solaris world)? I'm just asking, no need to focus on this for the answer :-) I would limit myself to these two options (SE11.1/OI) also because I will be making a NAS for me in the future (where high performances with Mac shares are also required) and Solaris has kernel support for AFP. I will use this server to gather experience as well. After this long question, thanks in advance! If you need additional info, let me know and I will update this post. UPDATES Given the first answers, I will strongly suggest the person paying the hardware to insert a second HD. Better 2x2TB than 1x3TB (3 TB is oversized anyway). I was trying to keep the initial costs down to spread them over a longer period, but better having something good from the beginning.

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