Re: RAID Stripe size

Hi


John A Meinel wrote:

>bm\mbn wrote:
>
>
>>Hi Everyone
>>
>>The machine is IBM x345 with ServeRAID 6i 128mb cache and 6 SCSI 15k
>>disks.
>>
>>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
>>setting.
>>
>>
>
>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.

>John
>=:->
>
>
>
>>Am i right ?
>>
>>
>
>
>

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