Messages in this thread | | | Date | Sun, 17 Apr 2005 11:53:21 -0400 | From | "Matt M. Valites" <> | Subject | Re: Poor I/O Performance with MegaRaid SATA 150-4; bug or feature? |
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Andre Tomt wrote:
> Matt M. Valites wrote: > >> Hail List, >> >> I've been banging my head against this for a few days, and I wanted to >> see if anyone here could lend a hand. >> >> I have the following configuration: >> P4 3.x Ghz >> 2GB Ram; >> 2 x 36GB WD Raptors; in a RAID1 (sda) >> 2 x 74GB WD Raptor (those 10K RPM SATA drives) in a RAID1(sdb) >> Two free PCI-X slots, one of which occupied by a LSI MegaRaid SATA >> 150-4. >> >> The problem is I/O on either one of these RAID devices seems to >> be less than half what I'm expecting. The file system used in my >> testing is >> XFS, and I'm running kernel 2.6.11.6. >> >> The test I'm doing is a simple: >> # time dd if=/dev/zero of=./crap.file bs=1024 count=209715 >> Which results in a runtime of about ~53s, in the best case, with all the >> scary write cache enabled. I've tried with deadline, and >> anticipatory. I've also tried several kernels, namely a recent 2.4, so >> I could test megaraid and megaraid2, similar results. >> >> On my desktop box, with one of these drives connected via SATA, i get >> ~25s, also XFS. (2.6.11-gentoo-r6 x86_64). >> >> Is this an expected result? I'm seeing much higher numbers posted >> around the >> 'Net. Most of those results are from Windows boxes. >> >> I've uploaded my kernel config, lspci -v, and two opreports of a >> bonnie++ run >> to: http://www.muixa.com/lkml/ > > > I also have one of those cards, at home. I've come to the conclusion > that they're just too old. No NCQ and such other fancy features (for > gods sake, the controllers on the card are sil 3112's!). It's probably > not even PCI-X native. > > The only thing that can bring its performance reseanably up to speed > is using write-back instead of write-through on the array. Also try > enabling the write-cache on the drives (all doable in the cards bios > config, not sure if this is what you meant with "with all the scary > write cache enabled"). Doing this is on the other hand not very good > for your data integrity, not good at all. > > If only NCQ/TCQ was in, it would have a chance of having decent > performance using write-through. A cool experiment would be setting up > the drives as invidual drives on the card, and use md software raid > over it. > > Next time I'll probably just use md software raid over a 3ware 9xxx > (JBOD-mode) or AHCI controller. I'm feeling quite uneasy about vendor > lock in nowadays. Groan. > Andre,
Thanks for the reply.
I wouldn't have expected NCQ/TCQ to have such an effect on a direct I/O test like dd. Even more disturbing, changing to a raid0 gives me close to the same results. When I enable write-cache, and "cached I/O" in the cards BIOS, i get results closer to a fast 7200RPM disk. Still nothing like the performance I know these raptors are capable of. Write-cache isn't an option for this machine, since it's slated to hold important version-control data :)
I could punt on this HW RAID idea, and just go with AHCI, but i've only got two ports free on the board. So, i need at least two more ports to pull it off, and I don't know of any SATA add-in card that has good driver support... Have you tested the RAID1 throughput of the 3ware 9x cards?
(this is why I still like SCSI... ) -- Matt M. Valites
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