Ext3 users - Mar 2004 - e2image, ext3 and nightly backups.

I have been looking at integrating the e2image tool into my nightly
backup routines for my systems, to improve the odds that I can get data
back if something disastrous happens to my file system.

I have a couple of questions about this, though, to work out if this is
actually worth doing.


Is e2image worth running if the file system is online and in use, under
the 2.6 series kernels, as part of a nightly backup run?

If there /is/ a risk of the data being incomplete or incorrect, is there
anything that can be done to make this less likely or to detect the
issue, other than adding LVM and using a snapshot to image from?


Does e2image capture all the information necessary to support ext3 file
systems?

It looks to capture everything except the journal content; will this
cause problems later if, say, the journal inode is destroyed but the
content isn't?  What if the journal inode /and/ content are destroyed?

Thanks for the advice,
       Daniel

-- 
Beware of all enterprises that require new clothes.
        -- Henry David Thoreau

Daniel Pittman <daniel at rimspace.net> wrote:
> Is e2image worth running if the file system is online and in use, under
> the 2.6 series kernels, as part of a nightly backup run?
Yes IMHO (but on other kernel versions, too).
> If there /is/ a risk of the data being incomplete or incorrect, 
There *is* (unless you can -o remount,ro before running e2image).
> is there
> anything that can be done to make this less likely or to detect the
> issue, 
The sledgehammer-method:

1. e2image to a file called a
2. e2image to a file called b
3. Compare the files - if they are identical you are done - remove file b.
4. remove file a
5. rename file b to file a
6. go on at step 2
> Does e2image capture all the information necessary to support ext3 file
> systems?
The only difference between ext2 and ext3 is the journal. It would be fatal 
to replay that some days later from a backed up version. So it's senseless 
at all to backup the journal.
> It looks to capture everything except the journal content; will this
> cause problems later if, say, the journal inode is destroyed but the
> content isn't?  What if the journal inode /and/ content are destroyed?
See above. In general e2image is no replace for e2fsck. If the filesystem 
gets really such horribly broken, that e2fsck cannot repair it, than the 
data captured via e2image can be used to rescue the files. But as that will 
make available only files which are some days old, you shouldn't bother 
about the journal at all. Think about it this way: In general you will 
never need the output of e2image at all. So if it is only a little bit 
incomplete (missing journal or something similar) it's not worth worrying 
about at all.

Regards, Bodo