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Date:      Tue, 2 Jan 1996 12:34:54 -0700 (MST)
From:      Terry Lambert <terry@lambert.org>
To:        eblood@winky.reno.nv.us (Eric Blood)
Cc:        questions@FreeBSD.org
Subject:   Re: NETBSD ccd driver
Message-ID:  <199601021934.MAA12378@phaeton.artisoft.com>
In-Reply-To: <199512292120.NAA00944@winky.reno.nv.us> from "Eric Blood" at Dec 29, 95 01:20:47 pm

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> What is the NetBSD ccd driver?

ConCatenated Disk driver.

It takes several drives, and makes them look like one drive.

With the devfs code in -current, there is a much cleaner way to
implement this sort of thing.  It's much more general, as well, so
you could use the full implementation to fix the disklabel and OS
compatability issues (magically).  These are all instances of
volume spanning and logical volume management.

I don't recommend ccd or striping unless you need it for some
serious application that you can't do any other way.  You end up
with a much lower MTBF on the spanned drives.

If you had three drives, your MTBF will be:

	min(min(MTBF1,MTBF2),MTBF3)
	---------------------------
		     3

Divide the one drive MTBF by the number of drives for identical
drives.


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.



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