What is ownblocks_calc scanner and how does it work?
Applies to
- ONTAP 9
Answer
- The snapshot is safely written to disk on the first consistency point after a snapshot command is issued.
- The size etc are computed after the phase by a slow
ownblocks_calc
scan that is deliberately throttled. - We run the
ownblocks_calc
when a snapshot is created, or blocks used complete (kicked off after a snapshot deletion) or if a list command is executed. - Further, since we only invalidate the values when
blks used
runs, it is possible that the values become quite stale untilblks used
finishes. - And
blks used
can get restarted every time a new delete occurs so it might take a long time for theownblocks
to get a chance to run & update the values, but there is no data integrity issue as far as the snapshot itself is concerned. - Running
wafl scan ownblocks_calc
from nodeshell forces us to recalculate own blocks values through the scanner even if they are valid/scan has not been kicked off through blocks used which is why you see updated values once this is executed.
Example output:
::> set advanced ::*> run local wafl scan status volume_name Volume volume_name: Scan id Type of scan progress 843657 block ownership calculation block 19994 of 30803
Additional Information
Snapshots size show 0KB in the command line and System Manager