Hello Richard, Thursday, February 22, 2007, 3:32:07 AM, you wrote:
RE> Nissim Ben Haim wrote: >> I was asked by a customer considering the x4500 - how much time should >> it take to rebuild a failed Disk under RaidZ ? >> This question keeps popping because customers perceive software RAID as >> substantially inferior to HW raids. >> I could not find someone who has really measured this under several >> scenarios. RE> It is a function of the amount of space used. As space used -> 0, it RE> becomes infinitely fast. As space used -> 100% is approaches the speed RE> of the I/O subsystem. In my experience, no hardware RAID array comes RE> close, they all throttle the resync, though some of them allow you to RE> tune it a little bit. The key advantage over a hardware RAID system is RE> that ZFS knows where the data is and doesn't need to replicate unused RE> space. A hardware RAID array doesn't know anything about the data, so RE> it must reconstruct the entire disk. RE> Also, the reconstruction is done in time order. See Jeff Bonwick's blog: RE> http://blogs.sun.com/bonwick/entry/smokin_mirrors RE> I've measured resync on some slow IDE disks (*not* an X4500) at an average RE> of 20 MBytes/s. So if you have a 500 GByte drive, that would resync a 100% RE> full file system in about 7 hours versus 11 days for some other systems RE> (who shall remain nameless :-) I wish it worked that good. raid-z2 made of 11 disks on x4500. When server wasn't doing anything - just resync, with pool almost full with lots of small files, it took about 2 days to re-sync. I think with lot of small files and almost full pool classic approach to resync is actually faster. With a server under some load (not that big) it took about two weeks! to re-sync disk. Then you've got to remember that you can't create new snapshots until resync finishes or it will start all over again and you never resync. This is known bug and very, very annoying on x4500 (or any other server). You should also keep in mind that current hot-spare support in ZFS is somewhat lacking - if write fails to a given disk system will panic instead put hot-spare in. Then after reboot depending on a disk failure type zfs will note disk is bad and use hot-spare or it will not (if it can still open that disk). Also if you have a failing disk (I had) you can manually initiate re-sync however until it finishes (two weeks???) you can't replace the old drive online as it needs to export an pool! You also can't detach a disk from raid-z[12] group until you re-sync new one. IMHO current hot-spare support in ZFS is very basic only and needs lot of work to be done. -- Best regards, Robert mailto:[EMAIL PROTECTED] http://milek.blogspot.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
