Data ONTAP and Space Management – Part 8

Let’s take a look at the snap autodelete command.  We will begin by checking the autodelete status:

The command: “snap autodelete vol1 show” returns the current status of the autodelete options for vol1.

By default, autodelete is turned off, so let’s start by turning it on:

It is now turned on.  The commitment option is set to try.  Either try or disrupt are available possibilities here.  This option controls which snapshots Data ONTAP will delete if it needs to recover space in the volume.  When set to try only snapshots which are not owned by data protection utilities may be deleted.  Data protection utilities include the dump command, ndmpcopy and the mirroring utilities.  Snapshots owned by backing utilities such as LUN or volume clones are also protected.   If the option is set to disrupt then snapshots which are not locked may be deleted.

The trigger option determines when the Data ONTAP will start deleting snapshots for that volume.  Trigger can be set to volume, snap_reserve or space_reserve.  If the trigger is set to volume, then once the volume has reached 98% of its capacity, it will begin deleting snapshots.  If the trigger is set to snap_reserve, then Data ONTAP will begin deleting snapshots when the volumes snapshot reserve is using 98% of its capacity.  The space_reserve option is a little more complex.  If the trigger is set to space_reserve than Data ONTAP begins deleting snapshots once the space reserved is at 98% capacity and the volume has used all of its snap reserve capacity.

Once Data ONTAP begins deleting snapshots it will continue until it reaches the value set in the target_free_space option.  It will apply this value against the “container” that reached the 98% threshold.  By default, this is set to 20% free space.  In our example, it would continue deleting snapshots until the volume had 20% free space available.

The delete_order option controls whether Data ONTAP will delete snapshots from oldest to newest or newest to oldest.  Valid values for this option are oldest_first or newest_first.

There may be some snapshots which we would like to avoid deleting if possible.  The defer_delete option will save these snapshots if possible.   Valid options are scheduled, user_created, prefix or none.  If we set this value to scheduled then snapshots that were created by Data ONTAP’s snapshot scheduler will be the last ones deleted.  If set to user_created than manual snapshots will be the last ones deleted.  If set to prefix, then snapshots whose names begin the prefix designated by the prefix option will be saved for last.  None means will are not trying to protect any particular classification of snapshots.

Finally, if we are trying to protect a class of snapshots by their name prefix, the prefix value is a string which contains the prefix name.  This string can be up to 15 characters long.

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