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ONTAP SAN Commvault Space Utilization Discrepancy Between Storage and Windows

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Applies to

  • NetApp FAS2820
  • ONTAP 9.14.1P7 (Cluster Mode)
  • Windows Server (NTFS)
  • Commvault backup application
  • iSCSI LUNs with space-allocation enabled

Issue

  • Significant mismatch in space usage reported between ONTAP clusters and Windows/Commvault replicated sites 
  • Aggregate utilization exceeds 80%, with very large LUN/VOL and daily data change rates
  • SCSI UNMAP (space reclamation) not occurring as expected or is severely delayed
  • Volume move and storage snapshots further increased space usage to critical levels
ONTAP output examples:

cluster1::*> lun show -path /vol/sql1_db/sql1_db -fields space-allocation,serial
vserver       path                 space-allocation   serial 
------------- -------------------- --------------------------
svm1_cluster1 /vol/sql1_db/sql1_db enabled       wOj5/?Yg/NFm
cluster1::> volume show-space sql1_db

      Vserver : svm1_cluster1
      Volume  : sql1_db

      Feature                                    Used      Used%
      --------------------------------     ----------     ------
      User Data                              4000.2MB         2%
      Filesystem Metadata                       636KB         0%
      Inodes                                     20KB         0%
      Deduplication                            2.35MB         0%
      Performance Metadata                      280KB         0%

      Total Used                             4030.4MB        40%

      Total Physical Used                    4440.2MB         2%

cluster1::> volume show-footprint sql1_db

      Vserver : svm1_cluster1
      Volume  : sql1_db

      Feature                                         Used       Used%
      --------------------------------             ----------    -----
      Volume Data Footprint                          4030.4MB      40%
      Volume Guarantee                                     0B       0%
      Flexible Volume Metadata                        13.38MB       0%
      Deduplication Metadata                           7.61MB       0%
           Deduplication                               2.29MB       0%
           Cross Volume Deduplication                  5.32MB       0%
      Delayed Frees                                  590.35MB       1%
      File Operation Metadata                             4KB       0%

      Total Footprint                                4830.8MB      50%

      Footprint Data Reduction                       390.98MB       0%
           Data Compaction                           390.98MB       0%
      Effective Total Footprint                      4430.8MB      41%

Windows Powershell output example: 

PS C:\Users\administrator.DEMO> fsutil behavior query disabledeletenotify
NTFS DisableDeleteNotify = 0  (Allows TRIM operations to be sent to the storage device)
PS C:\Users\administrator.DEMO> get-disk -Number 1,2
Number Friendly Name       Serial Number  HealthStatus  OperationalStatus  Total Size Partition
------ -------------       -------------  ------------  -----------------  ---------- ----------
1      NETAPP LUN C-Mode   wOj5/?Yg/NFm   Healthy       Online                  10 GB GPT
2      NETAPP LUN C-Mode   wOj5/?Yg/NFn   Healthy       Online                   5 GB GPT

PS C:\Users\administrator.DEMO> get-Volume
DriveLetter FriendlyName FileSystemType DriveType HealthStatus OperationalStatus SizeRemaining   Size
----------- ------------ -------------- --------- ------------ ----------------- -------------   ----
E           Data         NTFS           Fixed     Healthy      OK                    9.56 GB  9.98 GB
F           Logs         NTFS           Fixed     Healthy      OK                    4.89 GB  4.98 GB

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