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Trident backend option 'snapshotReserve' creates larger ONTAP volumes than expected

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Category:
trident-kubernetes
Specialty:
snapx
Last Updated:

Applies to

Astra Trident 21.07 and higher

Issue

  • When defining an ONTAP Trident backend to provide PVCs that also have snapshot capability, or where the volumes will run ONTAP based snapshots, a snapshotReserve can be set for every PVC under the defaults section of the backend.
  • When a PVC is requested with a certain size, the amount of space assigned to snapshot usage (and therefore total volume size) appears to be larger than expected if adding the snapshotReserve percentage to the requested PVC size [Total volume size = (PVC requested size) * (1 + (snapshotReserve percentage) / 100)]
  • Below is an example of the resulting volume size in ONTAP for a PVC specifying a 1GB volume based on different snapshotReserve percentages specified in the ontap-nas backend [setting a snapshotReserve of 100% is not possible (#DIV/0)]:
 

PVC
Size (GB)
PVC
snapshotReserve %
Percentage
ONTAP
snapshot-reserve-available (GB) 
ONTAP
Total Volume Size(GB)
    1     10 0.11 1.11
1 20 0.25 1.25
1 30 0.43 1.43
1 40 0.67 1.67
1 50 1 2
1 60 1.5 2.5
1 70 2.33 3.33
1 80 4 5
1 90 9 10
1 100 #DIV/0! #DIV/0!

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