Specifications

NetApp Deduplication for FAS and V-Series Deployment and Implementation Guide
30
Table 7) LUN configuration examples (as described below).
A (Default)
B
C
D
E
LUN space guarantee value
Yes
Yes
Yes
No
No
Volume fractional reserve
value
100
1-99
0
Any
Any
Volume thin provisioned?
No
No
No
No
Yes
After deduplication and thin
provisioning (if applicable), free
blocks are returned to:
Fractional
overwrite
reserve
Fractional
overwrite
reserve
+
Volume free
pool
Volume
free pool
Volume
free pool
Aggregate
free pool
DEFINITIONS
Fractional overwrite reserve: The space that Data ONTAP guarantees will be available for overwriting
blocks in a LUN when space guarantee = Yes. Behavior of the fractional reserve space parameter with
deduplication is the same as if a Snapshot copy has been created in the volume and blocks are being
overwritten.
Volume free pool: Refers to the free blocks in the parent volume of the LUN. These blocks can be
assigned anywhere in the volume as needed.
Aggregate free pool: Refers to the free blocks in the parent aggregate of the LUN. These blocks can
be assigned anywhere in the aggregate as needed.
LUN CONFIGURATION EXAMPLES
Configuration A: The Default LUN Configuration
The default configuration of a NetApp LUN follows. (Best practice for all NetApp LUNs is to turn controller
Snapshot off, delete all scheduled Snapshot copies, and set snap reserve to 0.)
1. LUN space reservation value = on Default = on
2. Volume fractional reserve Value = 100 Default = 100%
3. Volume guarantee = volume Default = volume
4. Snap reserve = 0% Default = 20%
5. Autodelete = off Default = off
6. Autosize = off Default = off
7. Try_first = volume_grow Default = volume_grow
Description: When a LUN containing default values is deduplicated, no apparent savings are observed by
the storage administrator because the LUN by default was ―space reserved‖ when it was created and
fractional reserve was set to 100% in the volume. Any blocks freed through deduplication are allocated to
the fractional reserve area. This configuration means that overwrite to the LUN should never fail, even if it is
overwritten entirely.
Pros and cons: The advantage of this configuration is that Snapshot copies consume less space when
blocks in the active file system are no longer being used. As a result, this volume can hold more Snapshot
copies. The disadvantage of this configuration is that free blocks are not returned to either the free volume
pool or the free aggregate pool. Moreover, there is no direct space saving in the active file system—in fact,
this configuration could consume more space in the volume due to new indirect blocks being written, if no
Snapshot copies exist in the volume and the Snapshot schedule is turned off.