Re: Are linux-fs's drive-fault-tolerant by concept?

[John Bradford]

> > > What is so bad about the simple way: the one who wants to write
> > > (e.g. fs) and knows _where_ to write simply uses another newly
> > > allocated block and dumps the old one on a blacklist. The blacklist
> > > only for being able to count them (or get the sector-numbers) in
> > > case you are interested. If you weren't you might as well mark them
> > > allocated and that's it (which I would presume a _bad_ idea). If
> > > there are no free blocks left, well, then the medium is full. And
> > > that is just about the only cause for a write error then (if the
> > > medium is writeable at all).
> >
> > Modern disks generally do this kind of thing themselves.  By the time
>                ^^^^^^^^^^^^
> How many times does Stephan need to say it? 'Generally do'
> is not enough, because it means 'sometimes they dont'.

OK, _ALL_ modern disks do.

Name an IDE or SCSI disk on sale today that doesn't retry on write
failiure.  Forget I said 'Generally do'.

> Most filesystems *are* designed with badblock lists and such,
> it is possible to teach fs drivers to tolerate write errors
> by adding affected blocks to the list and continuing (as opposed
> to 'remounted ro, BOOM!'). As usual, this can only happen if someone
> will step forward and code it.
> 
> Do you think it would be a Wrong Thing to do?

Yes, I do.

It achieves nothing useful, and gives people a false sense of security.

We have moved on since the 1980s, and I believe that it is now up to
the drive firmware, or the block device driver to do this, it has no
place in a filesystem.

John.