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From
SubjectRe: linux-2.4.10-pre5
Date
Followup to:  <Pine.LNX.4.33.0109091105380.14479-100000@penguin.transmeta.com>
By author: Linus Torvalds <torvalds@transmeta.com>
In newsgroup: linux.dev.kernel
>
> I agree that coherency wrt fsck is something that theoretically would be a
> GoodThing(tm). And this is, in fact, why I believe that filesystem
> management _must_ have a good interface to the low-level filesystem.
> Because you cannot do it any other way.
>
> This is not a fsck-only issue. I am a total non-believer in the "dump"
> program, for example. I always found it to be a totally ridiculous and
> idiotic way to make backups. It would be much better to have good
> (filesystem-independent) interfaces to do what "dump" wants to do (ie have
> ways of explicitly bypassing the accessed bits and get the full inode
> information etc).
>
> Nobody does a "read()" on directories any more to parse the directory
> structure. Similarly, nobody should have done a "dump" on the raw device
> any more for the last 20 years or so. But some backwards places still do.
>

The main reason people seems to still justify use dump/restore is --
believe it or not -- the inability to set atime. One would think this
would be a trivial extension to the VFS, even if protected by a
capability (CAP_BACKUP?).

The ideal way to run backups I have found is on filesystems which
support atomic snapshots -- that way, your backup set becomes not only
safe (since it goes through the kernel etc. etc.) but totally
coherent, since it is guaranteed to be unchanging. This is a major
win for filesystems which can do atomic snapshots, and I'd highly
encourage filesystem developers to consider this feature.

-hpa



--
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
http://www.zytor.com/~hpa/puzzle.txt <amsp@zytor.com>
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