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SubjectRe: e2fsck...
   Date: Fri, 13 Nov 1998 10:43:22 -0800 (PST)
From: David Lang <dlang@diginsite.com>

The Network appliance filers have a "snapshot" capability that works
somewhat similar to the following

1. when you take a snapshot the system makes a copy of all the inodes.

2. when a file is changed, the old inode and the block it points to are
left alone, the data is copied from the old block to a new block (with the
changes) and the current inode set is updated to match

the process of taking a snapshot is very fast and one it is taken the data
can be retreived as it existed at that time until the snapshot is deleted.
(the backup procedure for the network appliance takes a snapshot, backs it
up then deletes the snapshot)

This all happens on the same partition (although you can reserve some
space for snapshots, similar to how some disk space is reserved for root)

Yes, I'm familiar with this. But all of this presumes that your
filesystem metadata is sane. If the consistency of the filesystem
metadata (the inodes, etc.) are called into question, having this
"snapshot" capability doesn't necessarily help you in doing an on-line
salvage or fsck pass.

Riccardo's suggestion that you could make a snapshot of the filesystem
and then do a filesystem check on it won't help, therefore.

- Ted

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