iometer testing

The following is some notes i have around the parameters i usually use during testing. There is a good document at ixbt labs on the various tests and settings….

For a 1GB test set the sectors to : 2048000

Typical benchmarks; (which you will need to add)

128K 100% Read – Sequential

128K 100% Write – Sequential

Remember to bump the workers up to 5 or so. You can set the mixes across all the workers if you select the PC object.

http://ixbtlabs.com/articles/hddide2k1feb/iometer.html

zfs compression and latency

Since im using ZFS as storage via NFS for my some of my vmware environments i need to ensure that latency on my disk is reduced where ever possible.

There is alot of talk about ZFS compression being “faster” than a non-compressed pool due to less physical data being pulled off the drives. This of course depends on the system powering ZFS, but i wanted to run some tests specifically on latency. Throughput is fine in some situations, but latency is a killer when it comes to lots of small reads and writes (in the case of hosting virtual machines)

I recently completed some basic tests focusing on the differences in latency when ZFS compression (lzjb) is enabled or disabled. IOMeter was my tool of choice and i hit my ZFS box via a mapped drive.

I’m not concerned with the actual figures, but the difference between the figures

I have run the test multiple times (to eliminate caching as a factor) and can validate that compression (on my system anyhow) increases latency

Basic Results from a “All in one” test suite… (similar results across all my tests)

ZFS uncompressed:

IOps : 2376.68
Read MBps : 15.14
Write MBps : 15.36
Average Response Time : 0.42
Average Read Response Time : 0.42
Average Write Response Time : 0.43
Average Transaction Time : 0.42

ZFS compressed: (lzjb)

IOps : 1901.82
Read MBps : 12.09
Write MBps : 12.28
Average Response Time : 0.53
Average Read Response Time : 0.44
Average Write Response Time : 0.61
Average Transaction Time : 0.53

As you can see from the results, the AWRT especially is much higher due to compression. I wouldn’t recommend using zfs compression where latency is a large factor (virtual machines)

Note: Under all the tests performed the CPU (dual core) on the zfs box was never 100% – eliminating that as a bottleneck.