Defragmentation and Performance

[Sushil Sureka]

We have a mid size DB running on DB2 (approximate size of DB is 4 GB).
We noticed few days back that the disk is completely defragemented on
the server. Now we know that too much defragementation is not usually
good but I was wondering does anyone have any statistics on what kind
of impact does it have on the performance. We do have some performance
issue but probably it is for different reasons.

Thanks
Sushil

[Jean-David Beyer]

Sushil Sureka wrote:

We have a mid size DB running on DB2 (approximate size of DB is 4 GB).
We noticed few days back that the disk is completely defragemented on
the server. Now we know that too much defragementation is not usually
good but I was wondering does anyone have any statistics on what kind
of impact does it have on the performance. We do have some performance
issue but probably it is for different reasons.

Does it not depend on a lot of things. Are you running DMS or SMS? If SMS,
is your system one like Linux ext2 that is rather immune to fragmentation,
or is it something like Microsoft Windows FAT style that suffer greatly
from fragmentation? Why would defragmentation be bad? It might not be
worth the trouble to defragment, but I do not see it causing harm except
fortuitously where the fragmentation just happened to optimize rotational
latency time or something.

If the storage is SMS, then you will have to rely on DB2 to manage it
properly. Perhaps a REORG once in a while.

--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http://counter.li.org
^^-^^ 16:30:00 up 2:10, 3 users, load average: 4.18, 4.12, 4.09