Re: [Qemu-devel] Re: [PATCH][v2] Align file accesses with cache=off (O_DIRECT)

[Anthony Liguori]

Andreas Färber wrote:
> Am 21.05.2008 um 04:12 schrieb Anthony Liguori:
>
> > Jamie Lokier wrote:
> > > What do you imagine happens when you pull the power in the middle of
> > > writing a sector to a floppy disk (to pick a more easily imagined
> > > example)?
> > >
> > > There is not enough residual power to write the rest of the sector.
> > > That sector's checksum will therefore be corrupt, and (hopefully) have
> > > a CRC read error.  It can be written over again, wiping the CRC error.
> >
> > Why would the sector's checksum be corrupt?  The checksum wouldn't 
> > change after the data write.
>
> If you change part of the data but leave the checksum as-is, you'd 
> hopefully get a checksum mismatch... ;)

That's the point though, you're not changing part of the data.  You're 
rewriting the same data.  I don't think the checksum gets automatically 
invalidated whenever data is written to the disk.

Regards,

Anthony Liguori

> Andreas