Commit c53a381e authored by Mike Snitzer's avatar Mike Snitzer Committed by Alasdair G Kergon
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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: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent ecdb2e25

Documentation/device-mapper/snapshot.txt

+44 −0
Original line number Diff line number Diff line
@@ -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

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