John A Meinel wrote:

bm\mbn wrote:
Hi Everyone

The machine is IBM x345 with ServeRAID 6i 128mb cache and 6 SCSI 15k

2 disks are in RAID1 and hold the OS, SWAP & pg_xlog
4 disks are in RAID10 and hold the Cluster itself.

the DB will have two major tables 1 with 10 million rows and one with
100 million rows.
All the activities against this tables will be SELECT.

What type of SELECTs will you be doing? Mostly sequential reads of a
bunch of data, or indexed lookups of random pieces?
All of them. some Rtree some btree some without using indexes.

Currently the strip size is 8k. I read in many place this is a poor

From what I've heard of RAID, if you are doing large sequential
transfers, larger stripe sizes (128k, 256k) generally perform better.
For postgres, though, when you are writing, having the stripe size be
around the same size as your page size (8k) could be advantageous, as
when postgres reads a page, it only reads a single stripe. So if it were
reading a series of pages, each one would come from a different disk.

I may be wrong about that, though.
I must admit im a bit amazed how such important parameter is so ambiguous. an optimal strip size can improve the performance of the db significantly. I bet that the difference in performance between a poor stripe setting to an optimal one is more important then how much RAM or CPU you have. I hope to run some tests soon thugh i have limited time on the production server to do such tests.


Am i right ?

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