I understand why SCSI is used a lot for RAID, and I agree with you
that reliability is only one small reason.
You need to stop conflating IDE and SATA though (e.g. SAS is SATA phy
with SCSI command protocol over it - you sometimes can plug SATA
drives into SAS bays).
On Tue, 11 Sep 2007, Michael Watterson wrote:
> The reason for SCSI is:
> Decent HW RAID (most SATA/IDE "RAID controllers" are really SW RAID)
This hasn't been true for many years.
> Scaling: Easy to have lots of drives
This isn't true, even if measured against IDE. You can have lots of
IDE ports quite easily.
> Cheap Clusters: Easy to share SCSI drives between two controllers if
> different Host IDs
a) Electrically shared buses have certain problems.
b) It doesn't scale
Shared storage tends to be done with either SANs or network storage..
> Performance for multiuser (RAID 5, striping on a single bus works,
> IDE/SATA you need a separate controller for each drive to have 7
> drives executing different commands at once.
See second paragraph. This is waffle for SAS v SATA, where either you
use a SATA phy / disk, or you have a SATA multiplexer.
For parallel-SCSI, the shared bus is a SPOF. (Same for SATA/SAS
extenders, but you have a choice there).
> while a replacement drive is obtained. I doubt SATA is yet
> supporting true HW RAID5 and and Hot spares.. I could be wrong.
a) RAID has nothing to do with SATA/SCSI
b) You'd be wrong
Paul Jakma paul at clubi.iepaul at jakma.org Key ID: 64A2FF6A
He's just a politician trying to save both his faces...
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