questions about defrag

[marc seguin]

Does it mean something to perform a defrag operation on disk space located on a EVA disk array ?
I would say :
fsadm -e : no impact, for sure.
fsadm -d : possible impact

And does anybody have recommendations when performing a defrag on Oracle or Progress databases ?

Thanks

[Mel Burslan · Accepted solution]

first of all, I think the EVA disk array does its own optimization of data placement on the disk depending on how frequently a piece of data gets accessed.

Secondly, a lun is not a conventional hard disk to defrag. It is data scattered through multiple disk devices, presented to the os as a virtual disk device. What OS thinks the beginning of platter 1 sector 1 maybe (and most probably is) something totally different on the physical disk device itself. So, a defrag may do more fragmentation that it provides any benefit.

Also, all moder databases, which use filesystems for container files have an internal method of optimization of data placement. I don;t think you will gain any benefit by doing a defrag under your circumstances in MY OPINION. (the last words are intentionally in caps as I am no expert but presenting just a logical train of thought)

[A. Clay Stephenson]

Both -e and -d option could have possible, positive impacts but it has been my experience with vxfs filesystems that in almost all cases there was no significant (and often no measurable) improvement from doing this operation. Generally, database files and indices are preallocated often on brand-new filesystems and thus have no apprecable fragmentation. In any event, you can run these operations while the database is up.

If you expect a 2x improvement in your database performance then look elsewhere. If you expect possibly a 1.03x (or so) improvement then try it.

Remember, UNIX filesystems are designed from the "getgo" expecting to see thousands of files come and go rather quickly.

[Leif Halvarsson_2]

Hi,

Fragmentation can be at different "levels".

At the filesystem level, the type of storage system has no impact (local disk, SAN, EVA, XP etc.). Filesystem fragmentation will slow down performance in any case. Filesystem fragmetation problems is most likley on filesystems with a very large number of small files. Databases uses few, very large files and often preallocated space. fsadmin operates at filesystem level.

Fragmentation may also apply at disk systems. If I remember correct, an EVA system may be "fragmentated" is there is very little free space. There is no tool for this type of fragmentation, the solution is to add more disks.