Re: ext4 features

[Ric Wheeler]

Tomasz Torcz wrote:

> On Sat, Jul 01, 2006 at 07:47:16PM +0200, Thomas Glanzmann wrote:
>  
>
> > Hello,
> >    
> >
> > > Checksums are not very useful for themselves. They are useful when we
> > > have other copy of data (think raid mirroring) so data can be
> > > reconstructed from working copy.
> > >      
> > it would be possible to identify data corruption.
> >    
>
>  Yes, but what good is identification? We could only return I/O error.
> Ability to fix corruption (like ZFS) is the real killer.
>  

Having a checksum (or even a digital signature on a file) that lets us 
detect corruption is very useful since, in many cases, it allows us to 
flag the file as corrupt before it gets used.

In some cases, this is a big hint that you should restore it from backup 
(tape, other disk, etc).

I think that it is a generally useful thing even when not on a self 
correcting device,

ric

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