[Gllug] NFS problem

[Kostas Georgiou]

On Mon, Oct 22, 2007 at 08:18:48PM +0100, Nix wrote:

> On 22 Oct 2007, Kostas Georgiou told this:
> > You also risk data corruption with a soft mount
> > http://nfs.sourceforge.net/#faq_e4
> 
> Of course, take that with a pinch of salt, because you *also* risk data
> corruption with any disk medium which isn't at least battery-backed
> RAID, even if the machine as a whole is on a UPS, and how many of us
> have one of those?

For soft mounts I follow Neil's advice which is "Don't ever use soft
mounts" :) It's not hard to get in trouble with soft mounts, every time
the nfs server is slow (doesn't have enough free threads, is under heavy
load, you are rebooting it) for example instead of getting "nfs: server
foobar not responding, still trying" you'll end up with an I/O error.

The only time you don't risk data corruption with soft mounts is when
you export a read only fs read only to the clients. Keep in mind that
data corruption doesn't necessarily mean that you corrupted the copy
on the disk, it could just be that the nfs clients got the wrong data.

What is the point of using soft mounts anyway? Mounting with hard,intr
is a much saner option, I've never seen an application that can reliably
recover from an EIO yet.

I do have battery-backed RAID in my nfs servers btw :) 

> In practice if you keep reasonable backups, that sort of disk corruption
> is vanishingly rare.

Backups can not always save you from data corruption, by the time you
notice that a file is corrupted enough time could have passed that your
backups contain only the corrupted version.

Cheers,
Kostas
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