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Why is Write Anywhere File Layout (WAFL) reserve using a large percentage of my aggregate?

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ontap-9
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core
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Applies to

  Data ONTAP 7 and earlier 

Answer

Why is Write Anywhere File Layout (WAFL) reserve using a large percentage of my aggregate?

The following error appears in Operations Manager DataFabric Manager (DFM):

Aggregate aggr1 on Clustered filer1:
Aggregate Overcommitted.
Committed 1001 gigabyte(GB) (106.25%) out of 942 GB available; Using 846 GB
(89.79%) out of 942 GB available

filer1> aggr show_space aggr1
Aggregate 'aggr1'

Total space WAFL reserve Snap reserve Usable space
1097585664kilobyte(KB) 109758564KB 0KB 987827100KB

Space allocated to volumes in the aggregate

Volume   Allocated    Used       Guarantee
vol01    20977940KB   32872KB    volume
vol02    21009588KB   123108KB   volume
vol03    105985844KB  1230272KB  volume
vol04    20971564KB   12640KB    volume
vol05    52455700KB   1015896KB  volume
vol06    63019052KB   20861268KB volume
vol07    18965448KB   686548KB   volume
vol08    178261652KB  8886004KB  volume
vol09    209715564KB  16199256KB volume
vol10    10485804KB   340456KB   volume
vol11    52429180KB   214152KB   volume
vol12    10485804KB   30656KB    volume
vol13    765168KB     765168KB   volume(disabled)
vol14    3366916KB    3366916KB  volume(disabled)
vol15    98097384KB   98097384KB volume(disabled)
vol16    21032640KB   2026588KB  volume
vol17    60200KB      60200KB    volume(disabled)
vol18    10404KB      10404KB    volume(disabled)

Aggregate Allocated Used Avail
Total space 888095852KB 156959788KB 100641868KB
Snap reserve 0KB 0KB 0KB
WAFL reserve 109758564KB 35832KB 109722732KB

How can my system be over committed even though WAFL is only using 35832KB?

The WAFL filesystem reserves 10% of the aggregate space for metadata and performance. The space used for maintaining the volumes in the aggregate comes out of the WAFL reserve and the WAFL reserve can not be changed. Allocated space for flexible volumes as reported with aggr show_space is a sum of the reserve space for the volume and the space used by non-reserved data. In this example, several of the FlexVols on the aggregate have volume guarantees disabled allowing for thin provisioning which can lead to an overcommitted aggregate. An over-commited aggregate may not be cause for concern if it is the customer's intention to use thin provisioning.

Additional Information

See the following links for more information on NetApp Thin Provisioning: