What volume guarantees are

Volume guarantees (sometimes called space guarantees) determine how space for a volume is allocated from its containing aggregate-- whether the space is preallocated for the entire volume, for only the reserved files or LUNs in the volume, or whether no space at all is preallocated for the volume.

The guarantee is an attribute of the volume. It is persistent across storage system reboots, takeovers, and givebacks. Volume guarantee types can be volume (the default type), file, or none.

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A guarantee type ofvolume allocates space in the aggregate for the volume when you create the volume, regardless of whether that space is used for data yet. (This approach to space management is called thick provisioning.) The allocated space cannot be provided to or allocated for any other volume in that aggregate. This is the default type.

A guarantee of type volume provides the easiest management strategy-- the volume cannot run out of space before the amount of data it contains reaches the size of the volume. However, this manageability comes at the cost of increased storage requirements.

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A guarantee type of file allocates space for the volume in its containing aggregate so that any reserved LUN or file in the volume can be completely rewritten, even if its blocks are being retained on disk by a Snapshot copy. However, writes to any file in the volume that is not reserved could run out of space.

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A guarantee of none allocates space from the aggregate only as it is needed by the volume. Writes to LUNs or files (including space-reserved files) contained by that volume could fail if the containing aggregate does not have enough available space to accommodate the write. This approach to space management is called thin provisioning.

When space in the aggregate is reserved for the guarantee for an existing volume, that space is no longer considered free in the aggregate. Operations that consume free space in the aggregate, such as creation of aggregate Snapshot copies or creation of new volumes in the containing aggregate, can occur only if there is enough available free space in that aggregate; these operations are prevented from using space already committed to another volume.

When the free space in an aggregate is exhausted, only writes to volumes or files in that aggregate with preallocated space are guaranteed to succeed.

Note: Guarantees are honored only for online volumes. If you take a volume offline, any committed but unused space for that volume becomes available for other volumes in that aggregate. When you bring that volume back online, if there is not sufficient available space in the aggregate to fulfill its guarantee, you must use the force option, and the volume’s guarantee is disabled. When a volume's guarantee is disabled, this is reflected in the output of the volume show command.