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Date:      Sun, 28 Jan 2001 08:00:09 -0800
From:      Kirk McKusick <mckusick@mckusick.com>
To:        Garance A Drosihn <drosih@rpi.edu>
Cc:        arch@FreeBSD.ORG
Subject:   Re: Snapshots in the Fast Filesystem 
Message-ID:  <200101281600.IAA38768@beastie.mckusick.com>
In-Reply-To: Your message of "Thu, 25 Jan 2001 21:06:55 EST." <p05010400b69689d42373@[128.113.24.47]> 

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	Date: Thu, 25 Jan 2001 21:06:55 -0500
	To: arch@FreeBSD.ORG
	From: Garance A Drosihn <drosih@rpi.edu>
	Subject: Re: Snapshots in the Fast Filesystem
	Cc: Kirk McKusick <mckusick@mckusick.com>

	On Sept 23/2000, Barry Pederson wrote:
	>On July 05/2000, Kirk McKusick wrote:
	>  >
	>>  I have completed an initial implementation of snapshots for the
	>>  fast filesystem (UFS/FFS). I have put up a tarball on
	>>
	>>          http://people.freebsd.org/~mckusick/snap.tgz
	>>
	>>  I am looking for comments and feedback on these changes. I am
	>>  proposing to put them into 5.0-current on Tuesday July 11th
	>>  unless I get feedback indicating that folks are not happy
	>  > with this addition.
	>  >                    ....................
	>  > So, as you can see, this is definitely alpha-quality code.
	>>  Much remains to be done to make it really useful in
	>>  production systems. But, I wanted to let folks get a chance
	>>  to try it out and start reporting bugs.
	>
	>
	>I've been fooling with this in 5.0-CURRENT, and have have found
	>it to be a terribly, terribly cool feature.
	>        [...skipping...]
	>
	>Lastly, I'm curious if it's possible that snapshots will be MFC'd
	>into 4.x at some point? or will this be a 5.0 and up only feature?

	I thought I would stir the waters again and ask how this new
	feature seems to be working out in -current.  Is there much
	chance of it working with the 4.x-branch of releases?

	I realize there's a lot of work here, and that it may very well
	need to be tied into some of the smp-related work in 5.0 (wrt
	big-locks, etc), so I won't mind if it can't make it any sooner.

	Mainly I just wanted to reiterate that this sounds like a very cool
	feature (particularly given how huge disks are getting, a snapshot
	facility seems like a good use of that spare space), and that I'm
	looking forward to it whenever it does appear.

	-- 
	Garance Alistair Drosehn            =   gad@eclipse.acs.rpi.edu
	Senior Systems Programmer           or  gad@freebsd.org
	Rensselaer Polytechnic Institute    or  drosih@rpi.edu

Snapshots require a lot of hooks in the kernel to be fully functional.
In addition there are still several nasty bugs in them which need to be
worked through (I understand the problem, it is finding a clean fix
that is the problem). For these reasons, I do not expect them to be
MFC'd back to the 4.X kernel. I do hope to have them fully debugged
and operational by the time that 5.0 is released.

	Kirk McKusick


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