Cats wrote:
> Back in the bad old days, we put a lot of effort into attempting to
> balance the spindle load for SE databases, and to start with this
> practise has hung on with IDS databases.
>
> But is it really necessary now? We will be upgrading from 7.31 to
> (probably) 11.x, and it would be *so* easy just to have one huge
> dbspace for the application database (plus root dbspace, temp dbspace
> and so on). Is this a reasonable way to go now, performance-wise? It
> will certainly be easier to administer in terms of creating slices and
> so on, especially since we have a duplicate set on the development
> sever so adding a new slice on the live machine means adding one there
> as well.

I don't know much about SE but do know C-ISAM which I think is similar
in this regard. We have also done performance tests on both IDS and
C-ISAM applications.

C-ISAM databases date from the days when RAID controllers were too
expensive for many mid-range servers. Furthermore there were no cached
reads or writes (buffers) beyond OS caching and maybe a small hard disc
cache. Therefore disc performance is critical to these databases and
solid state discs, more disc controllers, more disc, a better load
balance, anything that improved disc performance helped greatly. As
there was often no RAID balancing spindles had to be done manually.

With IDS things are a little different. There are buffers, checkpoints,
cached reads and writes, and large amounts of memory available in modern
servers to facilitate these things. With IDS10 you can set DS_NONPDQ_MEM
high to avoid temporary dbspaces more often. Therefore writing and
especially reading from disc can be greatly reduced. We tried a solid
state disc with our application (which is OLTP and write-intensive) with
IDS and the performance lift was under 10%, which was very bad value for
money given the high cost of solid state. It's worth pointing out that
this small gain was against a RAID-10 set and fragment elimination and
other tricks were in use in both cases. With our C-ISAM product the lift
was enormous, I forget the exact figure now but 100% probably would be
in the right ball park.

I would expect any decent IDS installation these days to be using a
RAID-10 array in which case you would simply let the RAID controller
spread the load around the discs unless there was a good reason to do
otherwise. In your case if you wanted to create one big dbspace on top
of a RAID system performance would be just fine. If you don't have RAID
then you will still get some benefit from a good balanced disc layout,
it just isn't as critically important as it was.

Regards, Ben.