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DF may show logical space consumption

  1. Last updated
    Feb 21, 2025
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ontap-9
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core
Last Updated:
2/21/2025, 5:35:15 AM

Applies to

  • ONTAP Select
  • ONTAP 9.6

Answer

Article explains:

  • The user data (vol status -S) calculation
  • What does df take into account?
  • Gap between the df used / total used (vol status -S) and the physical used.

In this case, there are holes reserved as the customer was using CIFS, which uses file reservations.

Calculations
  1.  Use the following node shell command: 

> vol status -S

User Data is realized by subtracting the metadata (FS metadata + Inodes + Deduplication metafiles + quota metafiles + snap reserve - snap reserve unusable ) from the "total used" of the same command.

Example:

Volume : fsdebsgv5602_HyV_SQL_2
Feature                  Used         Used%
------------------------ ------------ ----------
User Data                896GB        13%
Filesystem Metadata      356MB        0%
Inodes                   524KB        0%
Deduplication            2.56GB       0%
Quota Metafiles          20.0KB       0%
Total                    899GB        13%
Total Physical Used      94.5GB       1%
Logical Used             6.01TB       86%
Logical Available        6.12TB       87%

899 GiB - 356 MiB - 524 KiB - 2.56 GiB - 20.0 KiB = 896 GiB

What does df take into account?
  • Delayed allocations
  • File reservations if any (hole reserves/overwrite reserves/cifs eof reserves)
  • Blocks reserved by flexible space pools for different operations.
  • PostCP saved counters: in-CP inline savings (packing/idedup) that cannot be released to general front-end use until the CP has its superblock safely on-disk.
  • Snapshot spill (blocks trapped in snapshots beyond snap-reserve).
The gap between df used and physical used
  • In case of an apparent huge difference between the df used and the physical used (vol status -S), it's mostly possible that there are file reservations that occur at volume level and not at aggregate level.
  • File/LUN reservations are the holes reserves and overwrite reserves, whose users are CIFS and LUNs. This can be understood using the fields in the stat show commands. 
  1. Start statistics for volume object: 

::> set advanced
::*> statistics start -object volume 
::*> statistics show -object volume <> -counter wv_fsinfo_blks_blks_rsrv_holes_cifs
::*> statistics show -object volume <> -counter wv_fsinfo_blks_blks_rsrv_overwrite
::*> statistics stop 

Example:

volume:vol1:wv_fsinfo_blks_blks_rsrv_holes_cifs:212453208
volume:vol1:wv_fsinfo_blks_blks_rsrv_overwrite:0

  1. The difference between in the df .used/ total used and the physical used can be realized by these hole reserved 212453208  blocks.

Additional Information

 

 

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