onlinejfs defrag

[Chris Rosenthal]

How safe is this? How far can I trust it? Do I need a backup immediately before I try it, or can I try it with confidence any time.

--Chris

[Scott Van Kalken]

I run one once a week, more of a hangover from my predecessor. I think thatit's not much use to do them honestly, but they're fine so long as the system is quiescent.

[James R. Ferguson]

Hi Chris:

This is regarded as fairly safe. However, it is wise to have a viable backup beforehand.

Once started, you should not kill the process. Remember that there are options to control the number of passes, etc. Consult the man pages for 'fsadm'. Remember, backups are worthless until you need one.

Regards!

...JRF...

[S.K. Chan]

Fairly safe I would say, if you are running the latest OnlineJFS version, system is fully patched, and very important the FS that you want defragment preferable not a FS that is almost full. For example doing a defragmentation on a say 90% full FS is risky since it needs the additional space for moving and relocating extents. Also if you really must defragment, do on a less busy time when the FS is not heavily accessed.

[A. Clay Stephenson]

On a well-patched system, if the filesystems are not near capacity, you should be fine. In fact, I have a cron job that runs weekly on my boxes and have never had a problem. Bear in mind that on filesystems that really change little (e.g Oracle data files & indices because these were preallocated), you are going to gain very very little. One option to consider, is to backup the filesystems, run a newfs, and then restore from backup. I would avoid running fsadm on a very busy filesystem; try to choose times when things are quiescent.

[harry_7]

Hi all,

Is it possible, First take full backup and delete the group and re-create the group restore from the fresh backup. In place of defrag. If possible make sure we have 2 sets of current full backup.

Regards

Harry

[George Petrides_1]

As Clay said, in filesystems with large Oracle files or small number of files you are not really going to see much of an improvement. However, if you have a filesystem with a large number of files then after using JFSonline to defragment it, you actually see a difference in performance. I was running it on weekly basis through the scheduler but I don't know what's going to happen if a machine crashes in the middle of defragmentation.
George