Re: [gentoo-user] Re: Fast checksumming of whole partitions

[Andrea Conti]

>> 1- if the root partition is [part of] what you're copying, you
>> *must* mount it read-only (mount -o ro /dev/sdc /work)
>
> Not from my experience; I simply mount, exec, and go - Works fine

Let's say you are 50% done copying a partition, when something writes to
it. If the write only affects the first half, which has alredy been
copied, the target will consistently reflect the "old" state; if on the
other hand the write only affects the second half, which has not been
copied yet, the target will consistently reflect the "new" state.
The problem is that with any write affecting both halves your copy will
contain a mix of the two states and thus will be inconsistent.

I am not saying that copying a rw-mounted partition will always fail:
you might be able to get away with it if nothing is actively writing to
the source partition. In any case you will not see any errors during the
copy.

andrea