Re: Raid0 slowdown from 2.4.19-rc1

From: Walt H (
Date: Mon Aug 05 2002 - 08:54:15 EST

Sorry, should have said more about raid arrays. Drives are partitioned
as follows:

hda1, hdc1 = 4GB
hda2, hdc2 = Extended part - remainder of drive
hda5, hdc5 = 2GB = raid1, md0 /boot
hda6, hdc6 = ~15GB = raid0, md1 /usr
hda7, hdc7 = ~15GB = raid0, md2 /home
hda8, hdc8 = 1.5GB = raid0, /
hda9, hdc9 = remainder = swap

I agree, it seems as though you could see preempt lower performance, but
again, I haven't seen that either. In fact, the 2.4.18 kernel I was
using before was compiled with preempt also and showed ~68MB/Sec on md1,md2.

As for changes I may have made to .config? Nothing new. 2.4.19-rc1
compiled with xfs and preempt worked well also. I tried looking for
differences in raid drivers, but there were none to the raid0 driver.
ide-pdc202xx.c contained many changes, but I'm not a kernel hacker and
couldn't spot anything that might have affected this. Odd that it shows
up even under hdparm. Interestingly, when testing with bonnie++, the
overall sequential output was similar to the higher performing older
kernels. However, creates, deletes, and rewrites were all down


Mark Hahn wrote:
>>Final 2.4.19 was patched with XFS and preempt and compiled using
> it's easy to imagine cases where preempt would produce lower performance,
> though I haven't seen any hard evidence of that.
>>cutting out preempt patches. First md1 array consists of two partitions
>>from hda & hdc. hdparm for both drives looks fine by themselves:
> are they the first two partitions in hda/c?
>> Timing buffered disk reads: 64 MB in 1.66 seconds = 38.55 MB/sec
>> Timing buffered disk reads: 64 MB in 1.65 seconds = 38.79 MB/sec
> such a disk will normally degrade to around half that performance
> in the tail of the disk.
>> Timing buffered disk reads: 64 MB in 1.44 seconds = 44.44 MB/sec
>>In 2.4.18 and up through 2.4.19-rc1 I saw 66-70MB/sec from this array.
>>Starting in rc2 it dropped to the mid 40's. I've also ran bonnie++ and
> nothing else changed?

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