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.
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? ;)

-- Mark Brinsmead
  Staff DBA,
  The Pythian Group

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