How to generate a large file allocating space

Alex Bligh alex at
Fri Nov 5 08:08:13 UTC 2010

--On 5 November 2010 00:05:45 +0100 Bodo Thiesen <bothie at> wrote:

>>    For instance, when a CoW snapshot is
>>    written to and expanded, the metadata must be written to, and there
>>    is no locking for that.
> Right, but that was not part of your use-case. If you need such things,
> you can't use ext4 as well.

I should have been clearer. We aren't using ext4 as anything other than
a block store. The CoW snapshots are done using our LVM replacement
type thing which stores metadata in such a way that it safe to access
it from multiple readers/writers. It would be lovely to use LVM for
this, but not (as far as I can tell) possible.

I might have another look at using lvm as a blockstore, then running our
stuff inside lvm. But I didn't think lvm was capable of running thousands
of LVs per volume group. ext4 is just fine for that. Perhaps I am
slating lvm unfairly.

Alex Bligh

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