Re: [Dump-users] Live filesystem summary

[Eric R. <ros...@ma...>]

Quoting Christopher Blunck <ch...@wx...>:

> I've researched dump and live filesystems all afternoon.

Either don't do it, or accept the slight possibility that you will have
non-stable file backups.  Which way to go depends on how busy your file
system is, which parts/files are busy, what your risk tolerance is, etc.

Personally, I've backed up live file systems for years with dump, and
never had a problem.  Mostly because I make daily backups, and people 
don't change files daily, so I figure I have a good copy of the file
on a tape somewhere.  But this is because most users don't change files
very often, and almost never during my backup window of 4AM to 6AM.

See below for my alternative for busy file systems.

> Recommendation #3:
>   Use LVM or EVSM "snapshotting" feature.
> Summary:
>   Although LVM/EVSM support snapshotting of filesystems, it is not
> immediately
>   apparent how you can tell dump to use the snapshot files (man dump does not
>   allude to "snapshot" or "hint" files).  Also, when I spoke with people on
>   IRC that use LVM, nobody has used this feature.

I use RHL 9 and LVM to do this on heavily modified file systems (like
/var/spool/mail for example).  It works well.  RHL/LVM allows you to mount
the snapshot readonly on any mount point.  So you just point dump at the
snapshot mountpoint, as you would with any other mount point.  No fuss,
no problems, simple.  Means that your disk is write-locked for about 1
second per night as it creates the snapshot, but processes just wait and
resume after that second, no real problem there.

I actually do this via amanda, which a "dump" shell script that handles
the amanda interface as well as creating the snapshot before the dump
and destroying the snapshot after the dump.

This is, IMHO, the best possible way to do backups. But, I only due
this on my busy/important file systems, since I'm lazy.  The rest I
dump normally, and know that I've never yet been burned because files
just don't change that often.

> I'd appreciate any feedback/comments on the above recommendations.  I may

If possible, and if needed, use LVM.  It rocks.

-- 
Eric Rostetter