Re: Back to the future.
From: Kyle Moffett
Date: Thu May 03 2007 - 12:54:57 EST
On May 03, 2007, at 11:10:47, Pavel Machek wrote:
How mature is freezing filesystems -- will it work on at least
ext2/3 and vfat?
I'm pretty sure it works on ext2/3 and xfs and possibly others, I
don't know either way about VFAT though. Essentially the "freeze"
part involves telling the filesystem to sync all data, flush the
journal, and mark the filesystem clean. The intent under dm/LVM was
to allow you to make snapshots without having to fsck the just-
created snapshot before you mounted it.
What happens if you try to boot and filesystems are frozen from
previous run?
If you're just doing a fresh boot then the filesystem is already
clean due to the dm freeze and so it mounts up normally. All you
need to do then is have a little startup script which purges the
saved image before you fsck or remount things read-write since either
case means the image is no longer safe to resume.
If the kernel is later modified to purge all filesystem data (dcache/
pagecache) during snapshot and effectively remount and reopen all the
files by path during restore then you could remove that requirement.
You'd just need to make sure that the restore-from-disk scripts did
an fsck or journal-restore before reloading the old kernel data.
Cheers,
Kyle Moffett
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