File system performance on HPUX 11.00

[CLUTIER]

Hi all,

I've got a performance problem on a file system of 36 GB made with 2 18.2 GB disks in an unique volume group (and a unique logical volume of course).

A simple shell with 'cp' and 'uncompress' command working on to files (170 and 75 MB) takes more than 10 minutes.

The same shell (working on the same files), running in another file system (a FS on an 18.2 GB disk) takes less than 2 minutes.

Does someone have any axplantion on this fact ?

Thanks for reply.

[Steven Sim Kok Leong]

Hi,

You could be running vxfs (or jfs) on one filesystem while hfs on another filesystem. The journal filesystem has a faster throughput (if you use default settings for both jfs and hfs filesystems).

If you happen to be using the same filesystem, it could also be due to differing filesystem block sizes or filesystem fragment sizes.

To compare the filesystem characteristics, run

# fsadm -F hfs full_path_of_your_lv

# fasdm -F vxfs full_path_of_your_lv

Run it on the filesystems you are comparing and compare the results.

Hope this helps. Regards.

Steven Sim Kok Leong

[Steven Sim Kok Leong]

Hi,

One other possible reason is due to how you conduct the I/O tests. During your first cp on one filesystem, the file is likely to end up in your cache. Thus, during your second cp test on another filesystem, it reads from the cache which is much faster.

Another possible reason is the freespace left in your filesystem. A filesystem reaching 100% full will degrade drastically in performance.

I don't think software RAID, number of disks on your disk controller and applications accessing each disk constitutes such a drastic difference in performance.

You can use sar or iostat and check the performance of the disks where the filesystems are residing on. If you have glance, you will be able to see the utilisation down to filesystem level.

Hope this helps. Regards.

Steven Sim Kok Leong
Brainbench MVP for Unix admin
http://www.brainbench.com

[Stefan Farrelly]

There is no performance difference from having 2x18GB drives in one LV order an LV with only a single 18GB drive.

Your performance difference must be due to either how busy the disks are at the time you do your copy (check by monitoring using sar -d) or how many files are on each of the LV's. The one with more files will be slower - depending on how many more files it has. Try an ls -R | wc -l on each lvol to see how many files are on them.