The stale fingerprints in the fingerprint database are not deleted; the excess data lingers and consumes space in the volume.
As more stale fingerprints accumulate, the increasing size of the fingerprint metadata increases the deduplication workload on the system, with the sorting and merging phases running for a long time. In aggravated cases, storage clients might experience a slow response.
This issue is more likely to be observed on a volume where there is a lot of file delete activity.
To determine if a flex volume on a storage system is experiencing this issue, the output of two administrative commands can be examined for numeric values from which a calculation can be made. The commands are:
sis check -c <vol>
sis status -l <vol>
Note: Run the
sis check command from the diag node.
The output of
sis check -c for a volume includes the following lines:
Checking fingerprint ... 18115836411 records
Number of Segments: 3
Number of Records: 18003077302, 53607122, 59151987
Checking fingerprint.vvol ... 56538330 records
Checking fingerprint.vvol.delta ... 2665604040 records
The important value is in the first line, the total of checked records, 18115836411, which will be called ‘TOTALCHECKED’ here.
In the output of
sis status -l for the same volume, the following line is included:
Logical Data: 3509 GB/49 TB (7%)
The important value is displayed first, the size of the logical data, 3509.
Take the logical-data size (in gigabytes) and apply the following calculation, which yields the number of storage blocks occupied by the logical data.
LOGICALBLOCKS = (LOGICALSIZE * 1024 * 1024) / 4
In this case,
(3509 * 1024 * 1024) / 4 = 919863296 is the LOGICALBLOCKS value.
To calculate the percentage of stale fingerprints, take the total of checked records from the
sis check -c output and use it in the following equation:
PERCENTSTALE = ((TOTALCHECKED - LOGICALBLOCKS) * 100) / LOGICALBLOCKS
In this case,
((18115836411 - 919863296) * 100) / 919863296 gives a PERCENTSTALE result of 1869.
As the result, 1869 is much larger than 20. The conclusion is that the triggering of
sis check at 20 percent stale did not occur, and thus the volume and storage system are experiencing the issue.