On Tuesday, 3 August 1999 at 8:12:17 +0200, Bernd Walter wrote:
> On Tue, Aug 03, 1999 at 12:16:06PM +0800, Stephen Hocking-Senior Programmer PGS
>Tensor Perth wrote:
>>
>>> No, it would cause a higher I/O load. Vinum doesn't transfer entire
>>> stripes, it transfers what you ask for. With a large stripe size, the
>>> chances are higher that you can perform the transfer with only a
>>> single I/O.
>>
>> Even if I'm using really large reads?
> Several month ago I beleaved the same but there are severall points here:
> - UFS/FFS don't handle clustering over 64k
> - modern harddisks do preread simply by having a reversed sector layout.
> - without spindle syncronisation you will have additional latency
> - vinum don't aggregate access to subdisks, so the transfer to the subdisks
> is limited by the stripe size.
Note, BTW, that this wouldn't make much sense. To aggregate access to
consecutive stripes, your transfer would have to involve *all* the
disks in the stripe set, which would be a ridiculous performance hit.
Read http://www.lemis.com/vinum/Performance-issues.html for more
details.
> For UFS/FFS there is nothing worth seting the stripesize to low.
> It is generally slower to acces 32k on different HDDs than to acces 64k on
> one HDD.
It is always slower where the positioning time is greater than the
transfer time for 32 kB. On modern disks, 32 kB transfer in about 300
�s. The average rotational latency of a disk running at 10,800 rpm is
2.8 ms, and even with spindle synchronization there's no way to avoid
rotational latency under these circumstances.
> Spindle Sycronisation won't bring you that much on modern HDDs - I tried
> it using 5 Seagate Elite 2.9G (5,25" Full-Height).
It should be useful for RAID-3 and streaming video.
Greg
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