[Gllug] A SATA Raid card worth having?

[Russell Howe]

On Fri, Jan 27, 2006 at 01:40:41AM +0000, Andy Farnsworth wrote:
> Russell Howe wrote:
> 
> ><snip>
> >
> >With SCSI, the bus speed is more important, since you can have perhaps
> >15 devices on a single chain (perhaps more? I'm not too up to date with
> >my SCSI knowledge). If you say your SCSI interface is 300Mbyte/s (U320,
> >say?), that's 20Mbyte/s per device.
> > 
> >
> This is why you use 15 drives on a SCSI chain :)  Each drive can easily 
> supply the 20+ Mb/s throughput so you can keep your 320 Mb/s pipe fully 
> saturated.

surely the aim is to never saturate the available bandwidth, so you'd
probably want to allow at least 50MB/s per drive (assuming nice fast 10
or 15k RPM drives). This limits you to about 6 drives per U320 SCSI
channel.

> with striping it gets worse not better as you have to wait for ALL the
> drives to reach r/w heads.

I saw a nice little feature on some SCA drives I have. They have a
little connector which you can daisy-chain to other drives. The drives
you've chained together will then synchronise their spindles, which
may well help many kinds of RAID. It's also a nice way to tie you into a
single vendor for drives :) (in this instance, I think it was Seagate)

I think it was targeted at companies using the drives in prepackaged
hardware RAID boxes (e.g. the kind of thing you can get from
DEC-then-Compaq-now-HP under their Storageworks brand and other similar
devices).

-- 
Russell Howe       | Why be just another cog in the machine,
rhowe at siksai.co.uk | when you can be the spanner in the works?
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