On Tue, Nov 20, 2001 at 08:40:13AM -0000, Wynne, Conor wrote:
> Much faster I would imagine. Software raid is going to have an overhead.
> I use Software RAID 1 (SCSI), its pretty fast and very reliable, but has
> a few percent CPU and RAM overhead.
OK - a little bit of clarification definitely needed here. First, all RAID
involves software of one sort or another for the various calculations
involved. When we speak of hardware RAID we generally mean a controller
which has a processor whereon the RAID software runs e.g. the SCSI RAID
controllers from DPT et al. The HPT-370 is NOT one of these. To use its
"hardware" RAID you need a special driver which provides a lot of the RAID
functionality and this driver, just like Linux software RAID, runs on the
host CPU and has, as Conor mentioned, a few percent CPU and RAM overhead.
Of course CPUs have become so fast now that your overall throughput may be
faster by sacrificing that few percent than by using the (typically) much
slower processor on the controller, though of course that processor has
nothing to do but RAID.
With a true hardware RAID controller, the host system doesn't know that
there is more than one disk attached. With SCSI the controller tells that
the host system that there is one (or more, depending on how you've
configured the disk with the controller's software) disk, which is actually
a RAID array, consisting of two or more disks.
With software RAID, and with that HPT-370 controller, the system sees more
than one disk and the host based software provides the RAID functionality.
The HPT is a little curious in that it does have a BIOS based setup utility
where you configure the RAID arrays yet when you boot the box in Linux you
still see hd? whatever, depending on how many disks you have. I've not used
the new driver, but as I said it's just another variation on software RAID.
I'd hope it might be faster than the standard Linux software RAID but I
don't know.
The box I have the HPT 370 on is in active service but it will be retired
soon, so if I get a while I might test it (but don't hold your breath).
Niall
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