Re: [gentoo-user] Ghosting a Ext3 partition

[Mark Kirkwood <markir@paradise.net.nz>]

Rasmus Andersen wrote:
>
> If you do backup live filesystems/data then dump is on par with dd; both
> read from the underlying device and might bypass the kernel's page cache.
> Ie., there might be unwritten data cached thats not on disk yet.
> Tar/rdiff-backup/etc reads through the pagecache and avoids this problem.
>
> The dump people talk a bit about this themselves on
>
>    http://dump.sourceforge.net/isdumpdeprecated.html
>
> Note I dont want to dis dump, backing up live filesystems is just tricky
> (depending on your consistency requirements :) and dump adds another
> level to that.
>
>
>   

Understood - I have seen that article too. I must say, I've mainly had 
experience with 'dump' on Freebsd and 'xfsdump' on Linux, and never had 
restore issues with *either* of these. Now I'm not sure whether these 
are supposed to be better than 'dump' on Linux aimed at ext2|3 
filesystems - certainly Freebsd's 'dump' has an option to tell it that 
it is dumping a 'live' filesystem, and the man pages for xfsrestore have 
notes concerning what happens when restoring an (xfs)dump from a 'live' 
filesystem - so they may well be!

On the other hand I've certainly routinely seen cases of people using dd 
(rsync, cpio, tar etc) and coming to grief at restore time. I am 
reluctant to suggest that folks use xfs and hence get access to xfsdump, 
as one of the nice things  about Linux is the  choice of a variety of 
filesystems - but it is pretty important to get able to backup of (for 
instance ) / ... and you usually don't have much option other than doing 
it live!

regards

Mark
 
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