Designing tablespaces with a SAN in mind

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James Conrad StJohn Foreman - 28 Jun 2006 18:59 GMT

Hi,

we've recently changed our db2 server from using a single RAID array to
a SAN. (machine is running 8.2.4 UDB on SLES 9, 2.6 kernel, 32 bit
Intel)

If we'd been using a RAID array, then we'd be tuning prefetch size
according to the number of discs and the stripe size. From what I
understand of the SAN configuration, there's an abstraction layer
between the physical storage and what gets presented to the machines
attached to it; eg there might be 50 discs in the SAN, but to the end
application it looks like either 1 disc, or 2 discs, or (potentially) a
RAID5 array with 6 discs, or any other permutation you care to think
of.

With that in mind, how should we be tuning the tablespace parameters?
Anyone have any pointers to useful documentation on this?

Thanks

JCSJF

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Ian - 28 Jun 2006 20:33 GMT

> With that in mind, how should we be tuning the tablespace parameters?
> Anyone have any pointers to useful documentation on this?

SANs should be no different than locally attached RAID arrays -- the
SAN just provides the connection between the host and storage array.
The fact that the storage array is typically HUGE, and may have a lot
of cache in front of it is just a detail.

Keep in mind that (no matter what the storage admins say), you should
have some understanding of how the storage is handled inside of the
storage device. i.e. are the LUNs presented to your system (which
appear as a single disk drive to the operating system) built on
5+P RAID5, 8+P RAID5, RAID-1 arrays, etc? What is the stripe size?
Are you getting more than 1 LUN from a single RAID array?

All of these things should play in to how you define your storage,
including extent size, prefetch size, NUM_IOSERVERS, DB2_PARALLEL_IO,
etc.

Most SAN vendors can provide best-practice white papers for using
their devices with DB2 (at least IBM, Hitachi, EMC and NetApp do.
Not sure about Compaq).

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