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Date: Wed, 10 Apr 1996 09:21:20 -0600
From: DARREND@novell.com (Darren Davis)
To: stable@freebsd.org
Cc: SCSI@freebsd.org
Subject: Disk Mirroring
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Is there a way to mirror two disks in FreeBSD?  The two different possibilities
are at the driver layer or at the filesystem layer.  I imagine the driver
layer would be the easiest.  Just take the block to be written and write
it out to both disks.  The reason I suggest the filesystem layer is to
avoid duplicating the swap space on both disks.  It would be cool if the
boot code could automatically deal with either disk failing and still having
the system boot.  Naturally, the driver should be able to deal with either
disk failing.  Has anyone given this some thought?  With disks getting
real cheap, it is a good way to have some fault tolerance with out the
cost or performance hit of RAID.  (Actually, I think mirroring is one form
of RAID.)

Darren R. Davis
Senior Software Engineer
Novell, Inc.