stijn at win.tue.nl
Sat Jan 22 01:00:55 PST 2005
On Fri, Jan 21, 2005 at 11:42:32PM -0800, Ted Mittelstaedt wrote:
> Stijn Hoop said:
> > "Ted Mittelstaedt" <tedm at toybox.placo.com> said:
> > > This did teach me a lesson that I kind of knew already but
> > > didn't think too much about. That is, a software array
> > > is no substitute
> > > for a hardware array. ...
> > I respectfully disagree here; it is a substitute in some respects,
> > especially if you factor in cost.
> I think you didn't read my post,
Well I tried to...
> I explicitly stated vinum is a great
> thing if what your wanting to do is use a bunch of cheap disks and
> cheap controller cards to either get a giant partition, or to
> stripe them together and get faster access.
Yes, but that's what I was refuting in part; I've used it for
reliability purposes to great effect, as I stated. So IMHO it's also a
great thing if you need reliability for a lower price.
> In other words cost is the only justification for selecting software
> raid over hardware raid. You haven't really made the case that vinum
> is better than a hardware array card on any other issue except cost.
It was not my intent to describe vinum as being 'better' than the
hardware RAID. As I read it, you dismissed software RAID for
reliability purposes. I was stating that it can be used for that
> > My vinum volumes allowed me to survive for a long time without backups
> > (bad idea, don't do that), and for the past years have allowed me to
> > survive without having to restore my backups. This through about 5
> > failing ATA disks and multiple upgrades of the storage space.
> > I'd say it was worth it for me, including reliability.
> > If you need speed, or have the cash, etc, you can go for hardware
> > RAID. But even there I've seen and heard horror stories of
> > incompatible disks, spontaneously lost configurations or even worse,
> > silent data corruption due to a bad disk.
> I didn't say these things couldn't happen on a hardware array. I
> said that when these things do happen, it's worse for a software
> array than a hardware array, and that they happen a lot more on a
> software array.
In my experience, when bad things happen, it was the same for the
software RAID arrays as for the hardware RAID arrays.
Regular vinum does have a few warts (notably, online rebuilding is
b0rked) but other than that it's the same procedure: remove bad drive,
add new drive, rebuild.
I agree that I've seen more failures with software RAID than hardware
RAID. And certainly cost is a factor in that. It still comes down to
cost vs downtime.
The only thing I 'objected' to in your post was the fact that you
dismissed vinum as being useful in reliability situations. I hope I
made that clearer this time.
"Well," Brahma said, "even after ten thousand explanations, a fool is
no wiser, but an intelligent man requires only two thousand five
-- The Mahabharata.
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