Re: ext4 features (salvage)

Helge Hafting
2006-07-04T12:46:58Z

On Tue, Jul 04, 2006 at 02:31:56PM +0200, Petr Tesarik wrote:
> On Tue, 2006-07-04 at 16:08 +0400, Lex Lyamin wrote:
> > you mean that blocks are naturaly free, but we cant use them because
> > someone may made them free by accident, but we cant use them...
> >
> > hmm...
> > great idea!
> >
> > wait, its not.
> > because of we cant use those blocks we cant optimise way we write one
> > disk , and if we have defragmenter we cant make use of them either.
> > and if (just if) this is online defragmenter, it cant use them too.
>
> Well, the way I saw it done was that you had no guarantee that any
> deleted file could be salvaged. Sometimes you even could salvage a file
> but not another one which was deleted later. Users seemed to be content
> with that, because in most situations it did help them restore files
> they deleted and within a few seconds realized that they didn't want to.
>
> This means that the allocator MAY purge any deleted block at any moment,
> although it tends to allocate blocks from areas of disk which haven't
> been used recently.
>
> And the benefits? The performance of such a filesystem could be better
> than snapshots, while allowing to cope with one of the most common human
> errors.

The most common error? A few years ago I restored a file from
backup, because I deleted it in error. I can't even remember
the second-last time I had that problem.

I'd say this error is among the easiest to avoid. :-)
Even a little performance loss won't justify it for me.

Now, there may be clumsier users than me, but they tend to
be using GUI "file managers" which do implement a "wastebasket"
for all internal deletion.

Helge Hafting