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Bug#351929: marked as done (FWD: (Severe?) Performance issues with ext3 created on RAID5 with partman)

Your message dated Tue, 27 Feb 2007 20:46:51 -0500
with message-id <20070228014651.GA1376@kitenet.net>
and subject line closing
has caused the attached Bug report to be marked as done.

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--- Begin Message ---
Package: partman-ext3
Severity: important

----- Forwarded message from Leo Bogert <spam-goes-to-dev-null@gmx.net> -----

From: Leo Bogert <spam-goes-to-dev-null@gmx.net>
Date: Wed, 8 Feb 2006 08:02:30 +0100
To: debian-boot@lists.debian.org
Subject: (Severe?) Performance issues with ext3 created on RAID5 with partman
X-Mailer: Microsoft Office Outlook, Build 11.0.6353


I recently installed the following system:
Celeron 2800 MHz 64 bit, running on an ICH7 board.
[3x 300GB SATA] <=> [sofware RAID5] <=> [loop-AES encryption] <=> [ext3fs]
running on Debian-amd64 testing, kernel

I created the RAID5 and ext3fs using the Debian installer.
Now my problem is: The read speed from the harddisks does not go over
exactly 51 MB/s. (mesured several times with different files by dd
if=/some-large-file of=/dev/zero)
When doing dd if=/dev/md1 of=/zev/zero I get almost exactly 100 MB/s though,
I also tried that with different offsets.
So the read speed of the RAID5 without any overhead added is 100 MB/s.
Now of course, one would first assume that the encryption is the bottleneck
because it uses much CPU power.
But I used /dev/shm to benchmark loop-AES also and it was at 270 MB/s.

The kernel uses the deadline IO scheduler and there were not any other tasks
running which use CPU while doing the benchmarks.
So obviously the bottleneck is the filesystem.
And I guess I also know the reason for this:

"There is a special option available when formatting RAID-4 or -5 devices
with mke2fs. The -R stride=nn option will allow mke2fs to better place
different ext2 specific data-structures in an intelligent way on the RAID

If the chunk-size is 32 kB, it means, that 32 kB of consecutive data will
reside on one disk. If we want to build an ext2 filesystem with 4 kB
block-size, we realize that there will be eight filesystem blocks in one
array chunk. We can pass this information on the mke2fs utility, when
creating the filesystem:

  mke2fs -b 4096 -R stride=8 /dev/md0"

Now I downloaded the partman-ext3 sources and there I did find a line doing
mkfs.ext3 which does NOT use the stride option. At that point I
unfortunately lost the motivation for digging deeper into the sources as it
will cost me enough work already to reinstall the complete system if it
really did not use stride :)  (That is no complaint, you are providing free
software. And I do like debian very much :)

So can someone tell me whether the debian installer really does not use the
stride option when formating ext3fs on RAID5? If so, please fix this as I
guess there could be many people who lose much performance because of that
without even knowing it. RAID5 setup is so easy with partman that they won't
read the HOWTO anymore.

And further, can someone tell me how I can format the partition myself with
the current debian installer? Maybe create everything with partman and then
say "no" when it asks to format the disks and then switch to the ALT+F2
consol, format them myself and switch back to the installer? Will it
continue correctly then if I have specified the right mount points and
filesystem options?
I don't want the hassle of creating a custom installation without installer.

Thanks in advance, Leo Bogert

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----- End forwarded message -----
see shy jo

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--- Begin Message ---
Maintainer seems to think notabug.

see shy jo

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