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dm: document when snapshot has finished merging 

Update Documentation/device-mapper/snapshot.txt to cover "How to
determine when a snapshot has finished merging".

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mike Snitzer 2010-03-06 02:29:56 +00:00 committed by Alasdair G Kergon
parent ecdb2e257a
commit c53a381efb
1 changed files with 44 additions and 0 deletions
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Documentation/device-mapper/snapshot.txt
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@ -122,3 +122,47 @@ volumeGroup-base: 0 2097152 snapshot-merge 254:11 254:12 P 16
brw------- 1 root root 254, 11 29 ago 18:15 /dev/mapper/volumeGroup-base-real
brw------- 1 root root 254, 12 29 ago 18:16 /dev/mapper/volumeGroup-base-cow
brw------- 1 root root 254, 10 29 ago 18:16 /dev/mapper/volumeGroup-base
How to determine when a merging is complete
===========================================
The snapshot-merge and snapshot status lines end with:
<sectors_allocated>/<total_sectors> <metadata_sectors>
Both <sectors_allocated> and <total_sectors> include both data and metadata.
During merging, the number of sectors allocated gets smaller and
smaller. Merging has finished when the number of sectors holding data
is zero, in other words <sectors_allocated> == <metadata_sectors>.
Here is a practical example (using a hybrid of lvm and dmsetup commands):
# lvs
LV VG Attr LSize Origin Snap% Move Log Copy% Convert
base volumeGroup owi-a- 4.00g
snap volumeGroup swi-a- 1.00g base 18.97
# dmsetup status volumeGroup-snap
0 8388608 snapshot 397896/2097152 1560
^^^^ metadata sectors
# lvconvert --merge -b volumeGroup/snap
Merging of volume snap started.
# lvs volumeGroup/snap
LV VG Attr LSize Origin Snap% Move Log Copy% Convert
base volumeGroup Owi-a- 4.00g 17.23
# dmsetup status volumeGroup-base
0 8388608 snapshot-merge 281688/2097152 1104
# dmsetup status volumeGroup-base
0 8388608 snapshot-merge 180480/2097152 712
# dmsetup status volumeGroup-base
0 8388608 snapshot-merge 16/2097152 16
Merging has finished.
# lvs
LV VG Attr LSize Origin Snap% Move Log Copy% Convert
base volumeGroup owi-a- 4.00g