[Gllug] moving system from one disc to another

Nix nix at esperi.org.uk
Fri Sep 3 07:19:31 UTC 2010

On 2 Sep 2010, James Hawtin spake thusly:

> On Thu, Sep 02, 2010 at 01:02:35AM +0100, Nix wrote:
>> On 31 Aug 2010, James Hawtin outgrape:
>> > You can dump and restore on a live system! 
>> Not safely (at least, you can't safely dump a mounted filesystem). dump
>> and restore access raw devices directly, and Linux's raw devices are not
>> cache-coherent with the filesystem: in particular, you can have pieces
>> of metadata inconsistently visible through the block device which have
>> actually been completely written to the device, or vice versa. That way
>> lies madness (at least it does if the filesystem is busy).
> Nothing else is going to be able to see changes either, all have problems

If you access the filesystem using the ordinary POSIX calls, it will be
able to see changes. If you do it directly from the block device, it may
miss anything that hasn't been flushed from the page cache yet.

> When I said Live I ment as in turned on, not as in people using it hard.

If you meant 'mounted' you are setting yourself up for a fall.
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