Benno Senoner wrote:
>
> Jan Edler wrote:
>
> > On Mon, Jan 10, 2000 at 12:49:29PM -0800, Dan Hollis wrote:
> > > On Mon, 10 Jan 2000, Jan Edler wrote:
> > > > - Performance is really horrible if you use IDE slaves.
> > > > Even though you say you aren't performance-sensitive, I'd
> > > > recommend against it if possible.
> > >
> > > My tests indicate UDMA performs favorably with ultrascsi, at about 1/6 the
> > > cost. Cost is often a big factor.
> >
> > I wasn't advising against IDE, only against the use of slaves.
> > With UDMA-33 or -66, masters work quite well,
> > if you can deal with the other constraints that I mentioned
> > (cable length, PCI slots, etc).
>
> Do you have any numbers handy ?
>
> will the performance of master/slave setup be at least HALF of the
> master-only setup.
Well, this depends on how it's used. If you were saturating your I/O
bus, then things would be REALLY ugly. Say you've got a controller
running in UDMA/33 mode, with two disks attached. If you have drives
that are reasonably fast, say recent 5400 RPM UDMA drives, then this
will actually hinder performance compared to having just one drive. If
you're doing 16MB/sec of I/O, then your performance will be slightly
less than half the performance of having just one drive on that channel
(consider overhead, IDE controller context switches, etc). If you only
need the space, then this is an accptable solution, for low throughput
applications. I don't know jack schitt about ext2, the linux ide
drivers (patches or old ones), or about the RAID code, except that they
work.
>
> For some apps cost is really important, and software IDE RAID has a very low
> price/Megabyte.
> If the app doesn't need killer performance , then I think it is the best
> solution.
It's a very good solution for a small number of disks, where you can
keep everything in a small case. It may actually be superior to SCSI
for situations where you have 4 or fewer disks and can put just a single
disk on a controller.
>
> now if we only had soft-RAID + journaled FS + power failure safeness right now
> ...
I'll be happy as long as it gets there relatively soon, I'll be happy.
fsck'ing is the only thing that really bugs me...
Greg
