Understanding quotas

Reasons for specifying quotas

You specify a quota for the following reasons:

To limit the amount of disk space or the number of files that can be used by a quota target
To track the amount of disk space or the number of files used by a quota target, without imposing a limit
To warn users when their disk space or file usage is high

Quota targets

A quota target can be

A user, as represented by a UNIX ID or a Windows ID.
A group, as represented by a UNIX group name or GID.
Note
Data ONTAP does not apply group quotas based on Windows IDs.
A qtree, as represented by the path name to the qtree.

The quota target determines the quota type, as shown in the following table.

Quota target	Quota type
user	user quota
group	group quota
qtree	tree quota

Tree quotas

If you apply a tree quota to a qtree, the qtree is similar to a disk partition, except that you can change its size at any time. When applying a tree quota, Data ONTAP limits the disk space and number of files regardless of the owner of the disk space or files in the qtree. No users, including root and members of the BUILTIN\Administrators group, can write to the qtree if the write causes the tree quota to be exceeded.

Quota specifications

Quota specifications are stored in the /etc/quotas file, which you can edit at any time.

User and group quotas are applied on a per-volume or per-qtree basis. You cannot specify a single quota for an aggregate or for multiple volumes. For example, you can specify that a user named jsmith can use up to 10 GB of disk space in the cad volume, or that a group named engineering can use up to 50 GB of disk space in the /vol/cad/projects qtree.

Explicit quotas

If the quota specification references the name or ID of the quota target, the quota is an explicit quota. For example, if you specify a user name, jsmith, as the quota target, the quota is an explicit user quota. If you specify the path name of a qtree, /vol/cad/engineering, as the quota target, the quota is an explicit tree quota.

For examples of explicit quotas, see Explicit quota examples.

Default quotas and derived quotas

Even if you do not specify an explicit quota for it in the /etc/quotas file, you can create default quotas to restrict or track the disk space used by a quota target,. If a quota is applied to a target and the name or ID of the target does not appear in an /etc/quotas entry, the quota is called a derived quota.

For more information about default quotas, see Understanding default quotas. For more information about derived quotas, see Understanding derived quotas. For examples, see Default quota examples.

Hard quotas, soft quotas, and threshold quotas

A hard quota is a limit that cannot be exceeded. If an operation, such as a write, causes a quota target to exceed a hard quota, the operation fails. When this happens, a warning message is logged to the storage system console and an SNMP trap is issued.

A soft quota is a limit that can be exceeded. When a soft quota is exceeded, a warning message is logged to the storage system console and an SNMP trap is issued. When the soft quota limit is no longer being exceeded, another syslog message and SNMP trap are generated. You can specify both hard and soft quota limits for the amount of disk space used and the number of files created.

A threshold quota is similar to a soft quota. When a threshold quota is exceeded, a warning message is logged to the storage system console and an SNMP trap is issued.

A single type of SNMP trap is generated for all types of quota events. You can find details on SNMP traps in the storage system's /etc/mib/netapp.mib file.

Syslog messages about quotas contain qtree ID numbers rather than qtree names. You can correlate qtree names to the qtree ID numbers in syslog messages by using the qtree status -i command.

Tracking quotas

You can use tracking quotas to track, but not limit, the resources used by a particular user, group, or qtree. To see the resources used by that user, group, or qtree, you can use quota reports.

For examples of tracking quotas, see Tracking quota examples.