Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 21 Apr 2003 11:32:36 +0200 | From | Stephan von Krawczynski <> | Subject | Re: Are linux-fs's drive-fault-tolerant by concept? |
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On Sun, 20 Apr 2003 18:20:16 +0100 (BST) John Bradford <john@grabjohn.com> wrote:
> > > > > Fault tolerance in a filesystem layer means in practical terms > > > > > that you are guessing what a filesystem should look like, for the > > > > > disk doesn't answer that question anymore. IMHO you don't want > > > > > that to be done automagically, for it might go right sometimes, > > > > > but also might trash everything on RW filesystems. > > > > > > > > Let me clarify again: I don't want fancy stuff inside the filesystem > > > > that magically knows something about right-or-wrong. The only _very > > > > small_ enhancement I would like to see is: driver tells fs there is an > > > > error while writing a certain block => fs tries writing the same > > > > data onto another block. That's it, no magic, no RAID > > > > stuff. Very simple. > > > > > > That doesn't belong in the filesystem. > > > > > > Imagine you have ten blocks free, and you allocate data to all of them > > > in the filesystem. The write goes to cache, and succeeds. > > > > > > 30 seconds later, the write cache is flushed, and an error is reported > > > back from the device. > > > > And where's the problem? > > Your case: > > Immediate failure. Disk error. > > > > My case: > > Immediate failure. Disk error (no space left for replacement) > > > > There's no difference. > > In my case, the machine can continue as normal. The filesystem is > intact, (with no blocks free). The block device driver has to cope > with the error, which could be as simple as holding the data in RAM > until an operator has been paged to replace the disk.
Forgive my ignorance, but I have not seen a case up to today where ide, aicX or 3ware has called me up for a replacement unit, written to it and been ok afterwards. What the heck are you talking of? I am not really interested in what a low-level driver could do unless there is none that does it... And again, how do you think this should work out on your _root_ partition? (see below)
> In your case, the filesystem is no longer in a usable state.
I have yet to see an fs thats in a writeable state after the medium is full ...
> If that > was the root filesystem, the machine will, at best, probably go in to > single user mode, with a read-only root filesystem.
How come?
> > Thing is: If there are 11 blocks free and not ten, then you fail > > Wrong. See above.
Please tell me when you were last "paged to replace the disk"? If you can't tell me, then you know I am right by now.
> > and I succeed (if there's one bad block). You loose data, I don't. > > John.
Regards, Stephan
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