Chalk it up to stupidity or just wanting to learn, but I don't
understand the prime number rationale. I'm sure there is a perfectly
legitimate reason, but I certainly don't know what it is. Could someone
enlighten those of us that are not stripe knowledgeable.
Chris Tooley
On Thu, 2002-10-31 at 16:30, Greg Freemyer wrote:
> >> On another mailing list a debate arose about performance over a single
> >> disk vs. multiple disks. It goes something like this:
>
> >> Suppose you have a 6 megabyte file stored on disk. Would it be read
> >> faster if it were stored contiguously on a single disk or spread over
> >> multiple (say 4) disks?
>
> >> It seems to me that as you get smaller it is faster for the single disk
> >> case (remember that we are assuming the file is stored contiguously - not
> >> spread all over the disk). At some size it seems natural that it would
> be
> >> faster if the file were spread over multiple disks. Can anyone comment
> on
> >> how XFS would perform? I don't have the equipment available to test
> this,
> >> but I'm not too concerned with actual benchmark numbers. Mostly I'm just
> >> wondering if I understand the filesystem correctly.
>
> >> James Rich
>
> James,
>
> I don't fully understand the logic, but I have a Compaq Storage Performance
> guide in front of me.
>
> For high data rate applications such as yours it recommends a stripe width
> (SW) of 17 sectors. It says that you want this small to get the spindles
> working in parallel, but if you go below 17, you start getting excessive
> overhead.
>
> i.e. 17 sectors of contiguous data per drive.
>
> For high request rate, it recommends the below stripe widths (SW):
>
> highly localized requests: SW = 10x avg. transfer size
>
> highly non-localized requests: SW = 20x avg. transfer size
>
> unknown localization: SW = 15x avg. transfer size.
>
> For all cases, they recommend your SW be a prime number. So the above just
> get you in the neighborhood and you select the closest prime number.
>
> Greg Freemyer
> Internet Engineer
> Deployment and Integration Specialist
> Compaq ASE - Tru64 v4, v5
> Compaq Master ASE - SAN Architect
> The Norcross Group
> www.NorcrossGroup.com
>
>
|