IO performance decreases after change to kernel 3.x

What is the output of:

cat /etc/issue; uname -a

Thanks

Please look at https://wiki.ubuntu.com/Releases and you will see that Ubuntu 10.04 has gone out of support a month ago.
It is strongly recommended that you upgrade your systems to a supported release.

a) Dell R710:

$> cat /etc/issue; uname -a
Ubuntu 10.04.4 LTS \n \l

Linux localhost 2.6.32-44-server #98-Ubuntu SMP Mon Sep 24 17:41:33 UTC 2012 x86_64 GNU/Linux

b) Dell R720: (I'm aware Ubuntu 10.04 is eol so I stayed with Ubuntu LTS 14.04 but the performance is still poor under Ubuntu 14.04)

$> cat /etc/issue; uname -a
Ubuntu 14.04.2 LTS \n \l

Linux localhost-v5 3.13.0-53-generic #88-Ubuntu SMP Wed May 13 18:10:29 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

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I can provide further information if needed.

Lucid is EOL and not supported in any way.

I suggest you upgrade to a newer (supported release). Trusty is the latest LTS and is supported til April 2019.

https://wiki.ubuntu.com/Releases

The new server (Dell R720) meanwhile runs with Ubuntu 14.04 Trusty but also shows the write performance issues in contrast to the tested 2.6.x kernels.

Even the recent upstream kernel 4.0.4 did perform poor (like the recent Trusty kernel too).

For test purpose I wrote directly to the device of the Dell R720 (Trusty) with a much better result.

#> uname -a
Linux localhost 3.13.0-53-generic #89-Ubuntu SMP Wed May 20 10:34:39 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

#> lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 14.04.2 LTS
Release: 14.04
Codename: trusty

#> dd if=/dev/zero of=/dev/vg0/lv_wo_fs count=10000 seek=20971520 bs=512 oflag=dsync
10000+0 records in
10000+0 records out
5120000 bytes (5,1 MB) copied, 0,80695 s, 6,3 MB/s

Does this imply that I'm faced with an filesystem issue? If this would be the case I would try to tweak some file system settings (data, barrier...).

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Here some further tests with different file systems for comparison:

#> blkid | grep lv
/dev/mapper/vg0-lv_xfs: UUID="ee63b8ec-227e-41d5-9115-23a149186dc2" TYPE="xfs"
/dev/mapper/vg0-lv_ext3: UUID="518e8f9d-81a9-4641-b9c8-9d07d2fc3212" TYPE="ext3"
/dev/mapper/vg0-lv_ext4: UUID="a800664a-8ba6-4bce-a133-a59089b8867c" TYPE="ext4"

#> dd if=/dev/zero of=/mnt/lv_ext3/dd count=10000 bs=512 oflag=dsync
10000+0 records in
10000+0 records out
5120000 bytes (5,1 MB) copied, 2,15098 s, 2,4 MB/s

#> dd if=/dev/zero of=/mnt/lv_ext4/dd count=10000 bs=512 oflag=dsync
10000+0 records in
10000+0 records out
5120000 bytes (5,1 MB) copied, 2,11697 s, 2,4 MB/s

#> dd if=/dev/zero of=/mnt/lv_xfs/dd count=10000 bs=512 oflag=dsync
10000+0 records in
10000+0 records out
5120000 bytes (5,1 MB) copied, 1,55431 s, 3,3 MB/s

After choosing the System Profile "Performance" [1] in Dell R720 BIOS I got some better values.

Unfortunately Dell seems to ship the BIOS with the System Profile "Performance-per-watt (DAPC)" which uses some power saving features.

Here the new results:

#> dd if=/dev/zero of=/dev/vg0/lv_wo_fs count=10000 seek=20971520 bs=512 oflag=dsync
10000+0 records in
10000+0 records out
5120000 bytes (5,1 MB) copied, 0,507091 s, 10,1 MB/s

#> dd if=/dev/zero of=/mnt/lv_ext4/dd_bla count=10000 bs=512 oflag=dsync
10000+0 records in
10000+0 records out
5120000 bytes (5,1 MB) copied, 1,28449 s, 4,0 MB/s

#> dd if=/dev/zero of=/mnt/lv_xfs/dd count=10000 bs=512 oflag=dsync
10000+0 records in
10000+0 records out
5120000 bytes (5,1 MB) copied, 0,885294 s, 5,8 MB/s

The values are still not as good as with 2.6.x kernel.

If I look at the values when writing to the volume without file system I don't understand where the huge loss of write speed (50-60%) comes when using ext4 (10,1 vs. 4,0).

[1] http://en.community.dell.com/cfs-file/__key/telligent-evolution-components-attachments/13-4491-00-00-20-24-87-40/12g_5F00_bios_5F00_tuning_5F00_for_5F00_performance_5F00_power.pdf

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