Re: Poor I/O Performance with MegaRaid SATA 150-4; bug or feature?

[Matt M. Valites]

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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