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Where did the 400Gig of vol capacity used come from?  Netapp 3140

Posted on 2012-09-21
Medium Priority
Last Modified: 2012-09-21
In the attached image you will see that Space used grew by 400GB yesterday.  Yet there is only one LUN in the volume and its size is 800GB while the Volume is 1.49TB.  Capacity Used on the volume is showing at 1.19TB.  BUT there are no snapshots as shown in the screen grab.  I did receive a message today with the controller complaining that it needed 110GB MORE space to create first snapshot.  So that would be part II to this question.  Why does this first snapshot require still more space?  Thank you.

"A Warning event at 21 Sep 10:19 Pacific Daylight Time on Volume
server_store_2 on Active/Active Controller heraklesa.pcmt.local:
Volume No First Snapshot.
Volume server_store_2 needs 110 GB more free space for creating first
Question by:amigan_99
LVL 22

Accepted Solution

robocat earned 2000 total points
ID: 38423630
You should read up on "fractional reserve" in the ontap manuals. It would take too long to explain in detail here, but in short:

Default behavior of a volume containing a LUN is that it will reserve 100% extra space compared to the space used by the LUN. The reserve space is used to prevent the volume from filling up when snapshots are taken. The volume should never ever fill up, or the LUN will go offline.

See the ontap manuals for a correct understanding of this feature. Think of it as a snapshot reserve of 100% for volumes that contain a LUN (which is quite wasteful).

You can set fractional reserve to zero in an environment that is closely monitored (eg using DFM/OM like you do), and make sure that the volume never fills up. This way you can use the available storage much more efficiently.

Or use snapshot autodelete combined with fractional reserve set to zero.

Author Closing Comment

ID: 38423692
Thank you.

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