Re: Raid Chunk Sizes for DSS type DB

On Tue, 30 Oct 2007 09:42:37 +0800
Ow Mun Heng <Ow(dot)Mun(dot)Heng(at)wdc(dot)com> wrote:

> It's not an optimal setup but since I only have 3x500G drives to play
> with, I can't build a Raid10, so I'm going for Raid5 to test out
> capability before I decide on Raid5 vs Raid1 tradeoff. (Raid1 = No
> Fault tolerance since 3 drives)
>

Uhhh RAID 1 is your best bet. You get fault tolerance (mirrored) plus
you get a hot spare (3 drives).

RAID 5 on the other hand will be very expensive on writes.

Joshua D. Drake

> Anyway.. I'm trying to figure out the chunk size for the raid. I'm
> using 4k chunks since I'm reading that for DSS type queries, lots of
> Large Reads, I should be using small chunks. [1] and I've aligned the
> disks per [2]
>
> and my stride will 3 for ext3
>
> mdadm --create --verbose /dev/md1 --level=5 --raid-devices=3
> --chunk=4 /dev/sdd1 /dev/sde1 /dev/sdf1 mkfs.ext3 -E stride=3 -O
> dir_index /dev/md1 mount /dev/md1 /pgsql/ -o noatime,data=writeback
>
>
> [1] http://wiki.centos.org/HowTos/Disk_Optimization
> [2] http://www.pythian.com/blogs/411/aligning-asm-disks-on-linux
>
> Just wondering if there's any suggestions/comments on this from the
> PG ppl here.
>
> Thanks for any/all comments.
>
>
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