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Re: [linux-lvm] Sparse LVs, --virtualsize equal to --size



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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