williamhathaway.com

I recently ran across a storage benchmark called Blogbench and decided to give it a quick whirl on my lab machine.

My environment consists of a Sun x4150 (32G RAM and dual quad-core Xeons @ 2.93 Ghz) running Solaris 10 05/2008 with (8) 73GB 10k RPM SAS drives and an LSI SAS RAID controller with 256M of memory.

For this test I created the following 6 disk zpool:

Two options I decided to test for ZFS using BlogBench were atime and compression.  For those unfamiliar with it, the atime of a file is changed when a file is accesed.  All UNIX file systems I’m aware of have atime updating enabled by default. As a sysadmin, it can be very handy to have the atime available to see when a file was last accessed, but  atime updating can add a significant amount of overhead in some access patterns, so a lot of sites disable it on mounts that need performance. For ZFS to disable atime you use:

zfs set atime=off $datasetname

for most UNIX file system types there is noatime or similar mount option that can be used.

I ran 5 iterations of BlogBench (using ./blogbench –directory=/data/blogbench ) for each permutation of atime and compression settings. I had the script sleep for 60 seconds between runs to make sure any background activity for memory or ZFS housekeeping had finished before the next run started.  Averaging the 5 runs together for each permutation gave me the following results:

When atime was on (which is the default), there was very little difference in the non-compressed versus compressed results.  With atime disabled there was a 30-50% increase in read transactions performed and about a 250% increase in write operations.  Note that the data size of the benchmark ( ~ 3.6G) was significantly smaller than the memory on the machine (32G) , so all reads were satisfied out of file system cache.

These results are only applicable to this specific test and software/hardware, so your environment may vary significantly but I would like people to be aware of the atime setting so they can be aware of another potential knob to turn in their environment.

This entry was posted on Saturday, April 4th, 2009 at 4:04 pm and is filed under solaris, zfs. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.