From: Pierre C <lists@peufeu.com>
To: Kenneth Cox <kenstir@gmail.com>
To: pgsql-performance@postgresql.org
Subject: Re: Advice configuring ServeRAID 8k for performance
Date: Fri, 06 Aug 2010 00:27:43 +0200
Message-ID: <op.vgzkohd0eorkce@apollo13> (raw)
In-Reply-To: <op.vgy9k5ov5ru9c3@kent60.office.vivox.com>
References: <op.vgy9k5ov5ru9c3@kent60.office.vivox.com>
> 1) Should I switch to RAID 10 for performance? I see things like "RAID
> 5 is bad for a DB" and "RAID 5 is slow with <= 6 drives" but I see
> little on RAID 6.
As others said, RAID6 is RAID5 + a hot spare.
Basically when you UPDATE a row, at some point postgres will write the
page which contains that row.
RAID10 : write the page to all mirrors.
RAID5/6 : write the page to the relevant disk. Read the corresponding page
from all disks (minus one), compute parity, write parity.
As you can see one small write will need to hog all drives in the array.
RAID5/6 performance for small random writes is really, really bad.
Databases like RAID10 for reads too because when you need some random data
you can get it from any of the mirrors, so you get increased parallelism
on reads too.
> with good redundancy. My current performance is 85MB/s write, 151 MB/s
> reads
FYI, I get 200 MB/s sequential out of the software RAID5 of 3 cheap
desktop consumer SATA drives in my home multimedia server...
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: lists@peufeu.com, kenstir@gmail.com
Subject: Re: Advice configuring ServeRAID 8k for performance
In-Reply-To: <op.vgzkohd0eorkce@apollo13>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox