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From: "Heinz J. Mauelshagen" <Mauelshagen@Sistina.com>
To: Michael Marxmeier <mike@msede.com>
Cc: linux-lvm@msede.com
Subject: Re: [linux-lvm] LVM 0.8final for 2.2.15/2.2.16?
Date: Thu, 8 Jun 2000 09:52:59 +0200	[thread overview]
Message-ID: <20000608095259.A2434@hmsysv.t-online.de> (raw)
In-Reply-To: <200006080022.CAA16063@e35.marxmeier.com>; from mike@msede.com on Thu, Jun 08, 2000 at 02:22:14AM +0000

On Thu, Jun 08, 2000 at 02:22:14AM +0000, Michael Marxmeier wrote:
> > 
> > On Wed, 7 Jun 2000, Jan Niehusmann wrote:
> > 
> > > The snapshot logic simply doesn't know what a filesystem is. It just
> > > clones the block device.
> > 
> > this i knew.. :)
> > 
> > > So the fs may be in en inconsistent state, if you do the snapshot
> > > while some write operation is in progress on the cloned
> > > filesystem.
> > 
> > ok. so the solution is what? a call in the vfs to complete pending
> > writes, and hold off on modifying any blocks?
> 
> IMHO when creating a snapshot LVM could simply sync all outstanding
> buffers for the block device vialog block_fsync() (not sure if this
> is already done -- Heinz care to comment?).

Yes, in case a new snapshot is created the buffers of the original LV
are flushed using fsync_dev(). Please have a look at the end of
lvm_do_lv_create() in lvm.c.

> This should also take care of pending fs meta information thus
> we should get a consistent state.
> 
> The question is how atomic this is? Since fsync_dev() currently
> does a lock_kernel() is might even be sufficient.

It should do the job (see comment bellow).

> 
> 
> Any reason why this is not suffiecient?

The only case could be any kind of "private" metadata a filesystem keeps
outside the cache.
Any comments on that?

Heinz

-- 

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Heinz Mauelshagen                                Sistina Software Inc.
Senior Consultant/Developer                      Bartningstr. 12
                                                 64289 Darmstadt
                                                 Germany
Mauelshgen@Sistina.com                           +49 6151 710386
                                                      FAX 710396
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

  parent reply	other threads:[~2000-06-08  7:52 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20000607100145.A6300@gondor.com>
2000-06-07 23:18 ` Paul Jakma
2020-11-27 16:17   ` Michael Marxmeier
2000-06-08  0:47     ` Paul Jakma
2000-06-08  8:23       ` Jos Visser
2000-06-08  8:34         ` Andi Kleen
2000-06-08 11:49           ` Paul Jakma
2000-06-08 12:34             ` Jos Visser
2000-06-09  6:59               ` Heinz J. Mauelshagen
2000-06-08  7:52     ` Heinz J. Mauelshagen [this message]
2000-06-06  9:51 Paul Jakma
2000-06-06 14:42 ` Andi Kleen
2000-06-06 22:30   ` Paul Jakma
2000-06-06 22:46     ` Andi Kleen
2000-06-07  0:03       ` Paul Jakma
2000-06-07  0:09       ` Paul Jakma
2000-06-12 13:20   ` Paul Jakma
2000-06-12 19:53     ` Jay Weber

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