> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of deg...@free.fr > > I'm not familiar with ZFS stuff, so I'll try to give you as much as info I can get > with our environment > We are using a ZFS pool as a VLS for a backup server (Sun V445 Solaris 10), > and we are faced with very low read performance (whilst write performance > is much better, i.e : up to 40GB/h to migrate data onto LTO-3 tape from disk, > and up to 100GB/h to unstage data from LTO-3 tape to disk, either with Time > Navigator 4.2 software or directly using dd commands) > We have tunned ZFS parameters for ARC and disabled preftech but > performance is poor. If we dd from disk to RAM or tape, it's very slow, but if > we dd from tape or RAM to disk, it's faster. I can't figure out why. I've read > other posts related to this, but I'm not sure what can of tuning can be made. > For disks concern, I have no idea on how our System team created the ZFS > volume. > Can you help ?
Normally, even a single cheap disk in the dumbest configuration should vastly outperform an LTO3 tape device. And 100 GB/h is nowhere near what you should expect, unless you're using highly fragmented or scattered small files. In the optimal configuration, you'll read/write something like 1Gbit/sec per disk, until you saturate your controller, let's just pick rough numbers and say 6Gbit/sec = 2.7 TB per hour. So there's a ballpark to think about. Next things next. I am highly skeptical of dd. I constantly get weird performance problems when using dd. Especially if you're reading/writing tapes. Instead, this is a good benchmark for how fast your disks can actually go in the present configuration: zfs send somefilesystem@somesnap | pv -i 30 > /dev/null (You might have to install pv, for example using opencsw or blastwave. If you don't have pv and don't want to install it, you might want to time zfs send | wc > /dev/null, so you can get the total size and the total time.) Expect the performance to go up and down... So watch it a while. Or wait for it to complete and then you'll have the average. Also... In what way are you using dd? dd is not really an appropriate tool for backing up a ZFS filesystem. Well, there are some corner cases where it might be ok, but generally speaking, no. So the *very* first question you should be asking is probably not about the bad performance you're seeing, but verifying the validity of your backup technique. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
