Re: Miserable Disks
- From: "Mark Brinsmead" <pythianbrinsmead@xxxxxxxxx>
- To: jkstill@xxxxxxxxx
- Date: Tue, 30 May 2006 20:04:30 -0600
Optimal for single session? Maybe. Isn't this roughly what RAID-2 was
supposed to do?
Of course, even then, it's really only optimal if the platters all spin and
the heads all move
synchronously, isn't it?
I was under the impression that this is why RAID-2 is rarely implemented.
(Normally,
I'd say "never implemented", but on this list, I just *know* somebody would
correct me...)
I don't know, really. Probably for single-session applications, especially
those doing huge
sequential I/O, you'd do quite nicely with just two or three of those
"Stinking Huge (TM)"
ATA disks that make us shudder whenever our PHBs mention them.
;-)
Sadly, I've never bothered to benchmark this configuration, but I *am*
pretty confident that
it will be far less-than-optimal for most concurrency levels much greater
than 1...
On 5/26/06, Jared Still <jkstill@xxxxxxxxx> wrote:
Comments inline.
On 5/25/06, Mark Brinsmead <pythianbrinsmead@xxxxxxxxx> wrote:
>
> (*) Make your RAID stripe width really narrow (like maybe 128 or 512
> bytes) and then
> make your database blocks large (like 8KB or 16KB) and do lots of
> multi-block I/O,
> so that every I/O is assured to engage every physical drive. (Kiss
> concurrency goodbye
> and watch your RIOPs numbers plummet)
>
Seems like somthing like this might be optimal for single session.
Benchmarks? ;)
--
Cheers,
-- Mark Brinsmead
Staff DBA,
The Pythian Group
http://www.pythian.com/blogs
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