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Posted by Brian Cryer on 05/24/05 17:37
"wriggs" <ian.w@btinternet.com> wrote in message
news:1116938928.959078.246100@z14g2000cwz.googlegroups.com...
> hmmm.. well i checked with the win2000 guys who originally setup the
> box and it seems both boxes are setup with raid 5, its just that the
> production box has got 8 drives in and the test box has 4 and obviously
> half the space, so could this be the problem as less data is being
> written to each individual drive on the production box??
>
> One other point to note is that the test box seems to have a better
> raid controller. the production one has a hp smart array 5300 where the
> test box has a 6400 controller.
>
> But obviously it isn't making that much difference
I think you've now answered your original question. If both are identical
systems, except the production one has an 8 disk raid 5 and the test one a 4
disk raid 5, then each disk write on the production system will be
distributed across 8 disks whereas on the test on it will be distributed
across 4 disks. The significant bit performance wise is that on your 8 disk
production system each disk only needs half as much data written to it as on
your 4 disk test box, and thus it should take about half the time - which is
what you are experiencing.
Personally I'm normally a bit sceptical about one controller being better
than another - if one has more ram on it then I can understand - but if you
are inserting a lot of records then once the cache becomes full then it
doesn't matter how large the cache is because you are still governed by how
fast the controller can stream the data to the disks. Also, if the
controllers are configured not to cache writes then it doesn't matter how
much ram they might have on them.
I know this isn't part of your question, but I assume that on both systems
when doing your data insert that the systems became disk bound - i.e.
disk/raid lights came on, stayed on and cpu usage fell away. In scenarios
like this it is the speed of your disks/raid which become the critical
factor. You could double the speed of your cpu and it wouldn't make any
difference.
Brian.
www.cryer.co.uk/brian
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