[linux-lvm] Sparse LVs, --virtualsize equal to --size
Marian Csontos
mcsontos at redhat.com
Mon Jan 28 13:50:48 UTC 2013
On 01/25/2013 09:44 AM, Vangelis Koukis wrote:
> On Thu, Jan 24, 2013 at 11:42:35pm +0000, Alasdair G Kergon wrote:
>> So look at thin provisioning with its zeroing option.
>> External origin. (support currently being added to lvm)
>>
>> Or this not-yet-upstream target:
>> http://people.redhat.com/agk/patches/linux/editing/dm-add-zeroed-target.patch
>>
>> Alasdair
>
> Thanks Alasdair,
>
> this seems to fit the bill perfectly, it's a shame it's
> not yet merged upstream.
>
> Until then, if we are to go with the "snapshot-over-the-zero-target"
> route, can you comment on quantifying the space overhead of tracking
> chunks in the snapshot?
Beware! Large old-style snapshots may take a very long time to
activate[1] (reportedly up to few hours) and my guess is many smaller
snapshots will behave the same[2], the total amount of chunks written to
all snapshots being the key to slow start...
You should definitely try it with your workflow before going too far
that direction.
[1]Just search for 'lvm large snapshot'. Someone here may be able to
point you to a more complete data.
[2] Not even trying to think about many larger ones as your usecase
suggests: just update kernel and java few times and with journal FS you
will soon be at few gigabytes per VM.
-- Marian
>
> Thanks again,
> Vangelis.
>
>
>
>
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