Re: [zfs-discuss] raid-z random read performance
I don't think you'd see the same performance benefits on RAID-Z since parity isn't always on the same disk. Are you seeing hot/cool disks? Adam On Sun, Nov 05, 2006 at 04:03:18PM +0100, Pawel Jakub Dawidek wrote: In my opinion RAID-Z is closer to RAID-3 than to RAID-5. In RAID-3 you do only full stripe writes/reads, which is also the case for RAID-Z. What I found while working on RAID-3 implementation for FreeBSD was that for small RAID-3 arrays there is a way to speed up random reads up to 40% by using parity component in a round-robin fashion. For example (DiskP stands for partity component): Disk0 Disk1 Disk2 Disk3 DiskP And now when I get read request I do: Request number Components 0 Disk0+Disk1+Disk2+Disk3 1 Disk1+Disk2+Disk3+(Disk1^Disk2^Disk3^DiskP) 2 Disk2+Disk3+(Disk2^Disk3^DiskP^Disk0)+Disk0 3 Disk3+(Disk3^DiskP^Disk0+Disk1)+Disk0+Disk1 etc. + - concatenation ^ - XOR In other words for every read request different component is skipped. It was still a bit slower than RAID-5, though. And of course writes in RAID-3 (and probably for RAID-Z) are much, much faster. -- Pawel Jakub Dawidek http://www.wheel.pl [EMAIL PROTECTED] http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am! ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss -- Adam Leventhal, Solaris Kernel Development http://blogs.sun.com/ahl ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] raid-z random read performance
I don't think you'd see the same performance benefits on RAID-Z since parity isn't always on the same disk. Are you seeing hot/cool disks? In addition, doesn't it always have to read all columns so that the parity can be validated? -- Darren Dunham [EMAIL PROTECTED] Senior Technical Consultant TAOShttp://www.taos.com/ Got some Dr Pepper? San Francisco, CA bay area This line left intentionally blank to confuse you. ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] raid-z random read performance
On 09 November, 2006 - Darren Dunham sent me these 0,7K bytes:
I don't think you'd see the same performance benefits on RAID-Z since
parity isn't always on the same disk. Are you seeing hot/cool disks?
In addition, doesn't it always have to read all columns so that the
parity can be validated?
If the block checksum is ok, then the parity is ok too.. I think?
(assuming checksum=on)
/Tomas
--
Tomas Ögren, [EMAIL PROTECTED], http://www.acc.umu.se/~stric/
|- Student at Computing Science, University of Umeå
`- Sysadmin at {cs,acc}.umu.se
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Re: [zfs-discuss] raid-z random read performance
Hello Robert, Thursday, November 2, 2006, 5:12:37 PM, you wrote: RM Hello zfs-discuss, RM Server: x4500, 2x Opetron 285 (dual-core), 16GB RAM, 48x500GB RM filebench/randomread script, filesize=256GB RM 2 disks for system, 2 disks as hot-spares, atime set to off for a RM pool, cache_bshift set to 8K (2^13), recordsize untouched (default). RM pool: 4x raid-z (5 disks) + 4x raid-z (6 disks) means that one pool RM was created wit 4 raid-z1 groups each with 5 disks and another 4 RM raid-z1 groups each with 6 disks. RM 1. pool: 4x raid-z (5 disks) + 4x raid-z (6 disks) RM(36 disks of usable space) RMa. nthreads = 1 ~60 ops RMb. nthreads = 4 ~250 ops RMc. nthreads = 8 ~520 ops RMd. nthreads = 128 ~1340 ops RM 1340/8 = 167 ops RM Now the same pool config but actual RAID-5 is done using SVM and zfs just does striping between SVM R5 devices. with nthreads=128 I get ~3680 ops which is almost 3x as much as with raid-z. I don't like this config but maybe it's a better way to go than with raid-z after all - at least with some environments. ps. however creating large file is about 4x slower than on raid-z -- Best regards, Robertmailto:[EMAIL PROTECTED] http://milek.blogspot.com ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
