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Date:      Wed, 9 May 2001 10:01:35 +0930
From:      Greg Lehey <grog@lemis.com>
To:        Douglas Egan <degan@calcon.net>
Cc:        dochawk@psu.edu, questions@freebsd.org
Subject:   Re: Raid
Message-ID:  <20010509100135.N68969@wantadilla.lemis.com>
In-Reply-To: <3AF8375C.DF2925C2@calcon.net>; from degan@calcon.net on Tue, May 08, 2001 at 01:13:48PM -0500
References:  <200105081646.f48GkIx16552@fac13.ds.psu.edu> <3AF8375C.DF2925C2@calcon.net>

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On Tuesday,  8 May 2001 at 13:13:48 -0500, Douglas Egan wrote:
> dochawk@psu.edu wrote:
>
>>> Which is why RAID 1 is superior, IMHO. Drives are bloody cheap today.
>>> Your data probably not (else you wouldn't be using RAID in the first
>>> place) so make it use the best.
>>
>> my understanding is that you can have a hot standby on RAID 5, so that
>> if a disk fails, it is replaced with the standby, leaving you protected
>> whileyou replace the offending drive.  But don't hold me to this; I
>> can't back it up (but we want to set up our new server like this).
>
> If vinum works like Linux raid, or NetBSD's RAIDFrame, when the hot
> standby is added into the array, reconstuction of the array starts
> taking place on the spare.  This can take a while and I believe if
> you lose another drive during this reconstruction phase, the array
> is gone.  I don't run with a hot standby so I don't know if
> reconstruction is automatic when a failure occurs or if you have to
> manually kick it off.

In Vinum, it's manual.  There are a number of reasons why automatic
rebuild isn't always desirable, but I'm planning to implement it as an
option.

> I have been using the RAIDFrame raid5 under NetBSD for about 6
> months now and it has worked great.  I scrapped Linux raid at that
> time.  I didn't like having to add patches at each kernel rev.
>
> I am going to bring up a FreeBSD system with vinum raid5 and see
> just how it compares to the RAIDFrame.

I'd be very interested to see the results.  As far as I know, nobody
has done this yet.  I'd be particularly interested in a comparison of
the performance.

Greg
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