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Storage : Volumes : Understanding volumes : What volume guarantees are
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 volume guarantee is an attribute of the volume. It is persistent across storage system reboots, takeovers, and givebacks. Volume guarantee values can be volume (the default value), file, or none.
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A volume guarantee of volume 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 value.
A volume guarantee of 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 volume guarantee of file reserves space for the volume from its containing aggregate so that any file in the volume with space reservation enabled 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 do not have space reservation enabled could run out of space.
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A FlexVol volume that has a volume guarantee of none reserves no space for user data; space is allocated from the aggregate on an as-needed basis, and 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 space 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 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 space guarantees are guaranteed to succeed.
Note: Volume 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 space guarantees, you must use the force option, and the volume’s space guarantees are disabled. When a volume's space guarantee is disabled, this is reflected in the output of the vol status command.