Re: RAID for the DB filesystem

2009/8/3 Scott Marlowe <scott.marlowe@gmail.com>
>
> On Mon, Aug 3, 2009 at 10:15 AM, Brian Modra<brian@zwartberg.com> wrote:
> > Hi,
> > my database is hit with constant inserts to 6 main tables (200 inserts
> > per minute to one of the tables, less to the others), some updates,
> > but then the selects:
> > - large retrievals of randomly different sections of the database
> > (indexed maps by postgis). This data is static.
> > - medium sized retrievals of the same tables that are receiving the
> > inserts. By mediou sized, I mean typically 200 rows at once. These
> > retrievals are also randomly different to each other, and typically
> > retrieving the newly inserted data rather than the more historical.
> > The database size is about 300GB and growing.
> >
> > What sort of hardware config would you advise?
> > I'm thinking of 2x300GB SATA RAID 0 for the OS and application files,
>
> Is there a valid reason you're NOT considering RAID-1 here?  I hope
> RAID-0 is a typo.

It was an error. I wanted mirroring. But... on second thoughts, is
there really a good reason for using a second set of disks for the OS?
Once the database is running, its surely not going to be using the OS
disk much, so why not just make a big RAID 10 array and use that for
both OS and DB... partition it as usual I mean - boot, root. Should I
use another disk for swap... for that matter, do I need swap at all...
RAM with be at least 16GB?

>
> > and 6x300GB SAS RAID 10 for the database... but some experts have said
> > RAID 5 is fine. I'm inlined to think RAID 10, but I'm not an expert.
> > Your advice will be much appreciated.
>
> Then I question the expertise of your experts.  RAID5 is not fine.
> It's slow, more prone to loss due to drive loss, and generally not a
> good choice for databases.
>
> I would gladly have more SATA drives in a RAID-10 than fewer SAS
> drives in a RAID-5.
>
> if someone is worried about "wasting" disk space tell them to worry
> about something else, like losing data.



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