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Re: [lvm-devel] master - python-lvm: Make second lv.snapshot() argument optional



Dne 16.12.2012 03:27, Andy Grover napsal(a):
On 12/15/2012 01:34 PM, Zdenek Kabelac wrote:
Dne 14.12.2012 23:11, Andy Grover napsal(a):
If no size is given, size defaults to 0, which in lvm_lv_snapshot will
allocate extents equal to the original LV be allocated for the new
snapshot.



Possibly not the ideal solution here.

1) we have some clash with command line 'API'
    user creates snapshot of thin volume
       - without giving size he get thin volume snaphost.
         lvcreate -s
       - with size specified he gets 'old' snapshot
         (snapshot outside of the pool)
         lvcreate -s -l|-L

Makes sense. So should we do the same for the Python API -- size = None
-> thin snap, size = >=0 -> 'old' snap with the given size? OR might we
even be OK with just supporting 'new' snaps, and get rid of the size
parameter altogether?


The 'old-snaps' should/will remain supported - since you may want to snap
data outside of the pool - i.e. you want limit maximum size the snapshot takes. Or you have very big 'chunk size' of the thin pool - and you may
want to take snapshot of the volume in that pool - so use of snapshot
with significantly smaller chunks size is preferable.

'zero' size snapshot (>=0) - I think this case is actually unsupportable - the minimum size for snapshot is I think 2 chunks (1 for data 1 for metadata) - so anything smaller should be rejected by metadata validator - so I think 0 should be equal to 'None'.

Zdenek


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