I/O Performance difference between SLES10 and SLES11 on ext3 mounted lvm devices
This document (7009219) is provided subject to the disclaimer at the end of this document.
SUSE Linux Enterprise Server 11
SUSE Linux Enterprise Server 11 Service Pack 1
During benchmarks, the iostat outputs shows high device utilization and low troughput, e.g.:
sda 0.00 0.00 0.00 0.40 0.00 0.00 8.00 0.01 18.00 10.00 0.40
sdaa 0.00 0.00 2.80 1458.20 0.01 11.38 15.97 4.04 2.78 0.68 100.00
vg_data-lv_lvol0 0.00 0.00 2.80 1458.00 0.01 11.38 15.97 4.03 2.77 0.68 100.00
This was done to improve data integrity and security on the file system, especially for local harddisks.
The drawback is that write barriers have a bad impact on write performance.
A detailed discussion of write barriers can be found here:
If write performance is a concern and data integrity is assured by the storage devices themselves (for example when using external storage arrays), you should disable write barriers.
This is done by passing the mount option:
to the file system. This can be passed as an option to the mount command, e.g.:
mount -o barrier=0 /dev/data/lvol0 /mnt
For automatic mounts, the entry in /etc/fstab is then:
/dev/data/lvol0 /mnt ext3 barrier=0 1 2
In SLES11 SP2 the issue has been addressed via code changes so that disabling of write barriers is not necessary anymore.
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- Document ID:7009219
- Creation Date: 22-Aug-2011
- Modified Date:03-Mar-2020
- SUSE Linux Enterprise Server
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