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Re: xfs_freeze same as umount? How is that helpful?

To: Linda Walsh <xfs@xxxxxxxxx>
Subject: Re: xfs_freeze same as umount? How is that helpful?
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Fri, 5 Oct 2012 09:32:04 +1000
Cc: xfs-oss <xfs@xxxxxxxxxxx>
In-reply-to: <506E1025.8050605@xxxxxxxxx>
References: <506DAB8C.9000601@xxxxxxxxx> <CAGpXXZJuWRAMnJfZKJMZ3N=0EwcfYOEwX+iteyk9hY7ojWA+XA@xxxxxxxxxxxxxx> <506E1025.8050605@xxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Oct 04, 2012 at 03:39:33PM -0700, Linda Walsh wrote:
> Greg Freemyer wrote:
> >Conceptually it is typically:
> >- quiesce system
> ----
>       Um... it seems that this is equivalent to being
> able to umount the disk?

NO, it's not. freeze intentionally leaves the log dirty, whereas
unmount leaves it clean.

> When I tried xfs_freeze / fs_freeze got fs-busy -- same as I would
> if I tried to umount it.

Of course - it's got to write all the dirty data andmetadata in
memory to disk. Freeze is about providing a stable, consistent disk
image of the filesystem, so it must flush dirty objects from memory
to disk to provide that.

> I thought the point of xfs_freeze was to allow it to be brought to
> a consistent state without unmounting it?


> Coincidentally, after trying a few freezes, the system froze.

Entirely possible if you froze the root filesystem and something you
rely on tried to write to the filesystem.

Anyway, a one-line "it froze" report doesn't tell us anything about
the problem you saw. So:



Dave Chinner

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