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SubjectRe: e2fsck...
On Thu, 12 Nov 1998, Theodore Y. Ts'o wrote:

> Multics did allow on-line salvaging of volumes, and it is theoretically
> possible to do such a thing. But it requires that the filesystem
> checker lock out kernel changes, and the filesystem checker would have
> to be in close communication with the kernel while it went about its
> business. E2fsck and the kernel both don't have the necessary
> infrastructure to do this today.

I recall that recently someone (I don't remember who just right now)
proposed some sort of snapshot device for filesystems. So that when you
access a snapshot you lock the filesystem and you can backup it. The
changes to the fs are recorded in a temporary partition (raw or e2fs or
the-same-as-the-shapshotted ?) and the /dev/sda1snapshot is synced, locked
and ready for backup (may be umounted ? Hmm ... I think better remounted
readonly). This way you can even 'e2fsck /dev/sda1snapshot'. Filesystem
snapshots seems a really good idea and the filesystem checker have not to
be in close communication with the kernel while doing its job.

Of course this raise a lot of other problems. For example what about
eating up all the temporary partition ? You have plenty of space on the
real partition but the temporary one is too little and fill up very fast.
The result should be a filesystem full or the kernel is allowed to
allocate more space on other partitions for saving the diff data ?


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