[Gllug] moving system from one disc to another

[Alain Williams]

On Thu, Sep 02, 2010 at 10:09:50AM +0100, t.clarke wrote:
> I assume that the only real doifference between the 'character' disk device
> on Unix and the 'block' disk device (on either Unix or Linux) is that writes to
> the character device go straight to the disk whereas writes to the block device
> go via a kernel blocking-buffer.  Sp presumably writes to the character device
> will be on the disk when the write completes whereas writes to the block device
> will only be there after the system has synced it (or it has been explictly
> synced or opened in sync mode).

Correct. However Linux does not have character devices for disks, tapes, ...

With character (raw) devices you also need to get block sizes right.

<pedant>
A write to the raw device does not do a kernel buffer, so you know that it is
with the device when the write() returns. However: many devices now have lots of buffer,
so for *complete* security you may need to do some device specific magic to ensure
that the data has been flushed to the brown stuff - to ensure that you are not
in a different sort of brown stuff if the power goes.
</pedant>

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Alain Williams
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