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


From: Anthony Liguori
Subject: Re: [Qemu-devel] Re: [PATCH][v2] Align file accesses with cache=off (O_DIRECT)
Date: Wed, 21 May 2008 09:06:30 -0500
User-agent: Thunderbird 2.0.0.14 (X11/20080501)

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







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