Re: Risks of backing up live mounted filesystems using dump(8)
- From: Dave Mitchell <davem@xxxxxxxxx>
- Date: Tue, 2 Mar 2010 13:59:23 +0000
On Tue, Mar 02, 2010 at 02:40:14PM +1100, Cameron Simpson wrote:
On 01Mar2010 21:30, Mike McCarty <Mike.McCarty@xxxxxxxxxxxxx> wrote:
| Yes, it is. I suspect he meant a files based backup. With
| dump, what one gets is a dump of the file system itself,
| as opposed to the data it contains. With a files based
| backup, one gets a copy of the data saved, but not the
| file system. So, for example, using tar, or cpio, one can
| back up a system using ext3, and recover to a system which
| uses reiserfs. One cannot do that with dump and restore,
| which store the file system itself. The dump and restore
| work at a lower level than files based backup.
I was pretty sure restore pulls "files" from the dump and writes to an
arbitrary filesystem (eg xfs or reiser etc). Dump accesses the filesystem
directly, but restore doesn't have that issue.
Yes, you are correct. Furthermore, although dump accesses the raw device
directly (and thus needs to know the specifics of ext*), the output of
dump is *not* tied to the file system format; it is instead a (fairly)
neutral format that consists of a series of records containing first, all
directory information, followed by the data and metadata for each file
being backed up (ordered by inode number). So, a file which is fragmented
and spread out across a disk will appear in the dump output as a single
blob.
Having all the directory info at the start of the dump means that it's
possible to quickly scan a backup to see if it contains the file(s) you're
looking for. restore even has an interactive mode for that purpose.
--
But Pity stayed his hand. "It's a pity I've run out of bullets",
he thought. -- "Bored of the Rings"
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- Re: Risks of backing up live mounted filesystems using dump(8)
- From: Mike McCarty
- Re: Risks of backing up live mounted filesystems using dump(8)
- From: Cameron Simpson
- Re: Risks of backing up live mounted filesystems using dump(8)
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