Date: Thu, 11 Apr 2002 16:50:22 -0700 From: David Drum <david@mu.org> To: FreeBSD DB List <freebsd-database@FreeBSD.ORG> Subject: Re: Raid configuration Message-ID: <20020411235022.GA21045@elvis.mu.org> In-Reply-To: <20020411180923.O56810@flake.decibel.org> References: <20020329113017.L51218-100000@zoraida.natserv.net> <20020411180923.O56810@flake.decibel.org>
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Quoth Jim C. Nasby:
> FWIW, RAID10 is not two seperate mirrors, it's a single volume. It's
> either a mirror of two striped volumes (yuck), or a stripe of mirrored
> volumes.
The first description you give is RAID 0+1, the second is RAID 1+0.
There is a difference. If a disk goes bad in a RAID 0+1, you've lost an
entire mirror, because the whole stripe is gone. If a disk goes bad in
a RAID 1+0, you've only lost one mirrored drive, and not a whole stripe.
mirror
+-------------+
|strpA strpB |
|+----+ +----+|
|| 1a | | 1b || RAID 0+1 (a mirror (RAID 0) of striped (RAID 1) drives)
|| | | ||
|| 2a | | 2b || If one disk in the "a" stripe goes bad, the whole stripe
|| | | || is lost. So no matter how many disks are in the RAID,
|| 3a | | 3b || the loss of one results in a practical loss of 50%.
|+----+ +----+|
+-------------+
stripe
+-------------+
| mirror1 |
|+-----------+|
|| 1a 1b || RAID 0+1 (a mirror (RAID 0) of striped (RAID 1) drives)
|+-----------+|
| mirror2 | If any one disk in any of the three mirrors goes bad,
|+-----------+| the stripe is still preserved.
|| 2a 2b ||
|+-----------+|
| mirror3 |
|+-----------+|
|| 3a 3b ||
|+-----------+|
+-------------+
Regards,
David Drum
david@mu.org
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