Re: Hardware RAID

From: Stijn Hoop (stijn_at_win.tue.nl)
Date: 01/22/05

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    Date: Sat, 22 Jan 2005 10:00:52 +0100
To: Ted Mittelstaedt <tedm@toybox.placo.com>

    On Fri, Jan 21, 2005 at 11:42:32PM -0800, Ted Mittelstaedt wrote:
    > Stijn Hoop said:
    > > "Ted Mittelstaedt" <tedm@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
    purpose.

    > > 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.

    --Stijn 

    -- 
"Well," Brahma said, "even after ten thousand explanations, a fool is
no wiser, but an intelligent man requires only two thousand five
hundred."
                -- The Mahabharata.

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