swapping LVs about

Alexander Skwar listen at alexander.skwar.name
Sun Sep 3 12:40:59 UTC 2006


· Gabriel M Dragffy <dragffy at yandex.ru>:

> I also have something that I don't understand. My root partition is 300M
> and has used about 170M of space. I created a 100M snapshot volume of it
> and it worked - how come it had enough space? How much space does a
> snapshot actually need,

0 - zero

> or more simply how does the snapshot work?

When you create a snapshot volume, you take, well..., a snapshot
of the volume. This means, at a later time, you can see how the
volume looked like at the moment, when you took the snapshot.

Now, to do so, if something gets written to the original LV, LVM
needs to somehow note the differences. And that's where the size
of the snapshot LV comes into play. If you've got a 100M snapshot
LV, you'll be able to write up to 100M to the original LV. After
that, the Snapshot LV is full.

Alexander Skwar
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