Re: Raid5 Read Perf drop in 2.6.27

Would you mind attaching both kernel config files and emailing them?
Also, did you compile your own kernels or do you run certain images?

On Wed, Sep 16, 2009 at 11:19 AM, Majed B. [off-list ref] wrote:

I've run my own tests a few days back on a machine I have, but I
haven't compared the results to tests on the same machine with older
kernels.

I have attached my machine's kernel config file.

I run an Ubuntu 9.04 Server - Kernel 2.6.28-15-server.

On Wed, Sep 16, 2009 at 11:10 AM, Linux Raid Study
[off-list ref] wrote:

quoted

Yes - as far as Raid/disk-controller stuff is concerned, they are
same. BTW, is there anything specific you would like me to check.

Have you done similar tests? Do you see any perf drop?

Thanks!

On Wed, Sep 16, 2009 at 1:06 AM, Majed B. [off-list ref] wrote:

quoted

Did you compare both kernel's config files to see whether these
kernels have been compiled with different options?

On Wed, Sep 16, 2009 at 10:57 AM, Linux Raid Study
[off-list ref] wrote:

quoted

Hi Majed, All:

I'm using the default scheduler with 2.6.21 and 2.6.27...do you know
if there is any difference?

I rechecked the perf today - everything (i.e. disks, disk controller
etc) remaining the same, I see around 45MB/s difference in performance
when I change kernel from 2.6.21 to 2.6.27. I issue following cmd to
see performance:
hdparm -t /dev/md0

FYI...I'm using Seagate HDDs (7200 RPM) with RocketRaid 2310 controller.

Any ideas...I have tried blockdev readahead option and it helps but
still not enough...

Thanks a lot!

On Wed, Sep 9, 2009 at 4:52 PM, Majed B. [off-list ref] wrote:

quoted

Are you sure you're using the same Kernel Scheduler on both kernels?

Have you checked and verified that the same drivers are being loaded?
(IDE vs. AHCI -- proprietary drivers vs. open source)

This is interesting!

On Thu, Sep 10, 2009 at 1:54 AM, Linux Raid
Study[off-list ref] wrote:

quoted

Hello:

I'm benchmarking RAID5 Read performance with 4 disks and notice perf
drop when using kernel 2.6.27.
The perf with 2.6.27 is 150MB/s whereas with kernel 2.6.21 (and same
setup), the perf is 180MB/s/



Some of the tests I have done:
1. I ran  experiments using iozone also but notice that READ perf with
RAID5 in 2.6.27 is ~30% less as compared to 2.6.21.
Write perf is similar but Read is an issue.

2. On 2.6.27, I played around with chunk size and blocksize parameters
and got ~5% improvement but not much. I used following cmds:

#mdadm --create /dev/md0 --level=5 --assume-clean --raid-devices=4
/dev/sda /dev/sdb /dev/sdc /dev/sdd --chunk=32
#mke2fs -b 4096 -E stride=8 /dev/md0

#time dd if=/dev/md0 of=/dev/null bs=94208 count=1024


Is this perf drop a known issue? Can someone please recommend some
performance tuning tips?

Thanks a lot for your time and help!
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