Understanding data management

Understanding volumes and qtrees

What volumes and qtrees are

A volume is a file system on a filer. Each filer has a special volume known as a root volume. The root volume contains a file known as the /etc/rc file, which contains startup commands. There can be only one root volume on a filer.

A qtree is a special subdirectory of the root directory of a volume. There are no special qtrees.

When creating volumes is appropriate

You can create up to 199 additional volumes when you want to treat large amounts of data as a unit. You create one or more additional volumes under the following circumstances:

A volume has more disks or storage than it is convenient to manage as one unit.
You want to accommodate users with different security styles or oplocks requirements that current volumes do not meet and you do not want to create a qtree for that purpose.
You have a multilingual environment and want to provide one volume for each language and character set.

If your filer has a large number of disks, creating volumes and having a multivolume configuration can also aid in administration. Having multiple volumes enables you to do the following:

Perform administrative and maintenance tasks, for example, backup and restore, on individual volumes rather than on a single, large file system.
Set vol option command values, for example, snap sched, raidsize, minra, no_atime_update, and so on, differently for individual volumes.
Take individual volumes off-line, for example, to perform administrative tasks on them while the other volumes remain on-line, without interrupting data availability.
Have more flexible quota and snapshot configurations.
Have backups and restores of individual volumes, which take less time.

However, there is a trade-off: you must use additional disks as parity disks and hot spares rather than for data storage.

When creating qtrees is appropriate

You create qtrees for amounts of data that do not expand the size of volumes unduly. You can set up qtrees and remove them easily. However, there is a trade-off. Because qtrees are part of a volume, they inherit many volume-level settings.

Detailed comparison

Qtrees and volumes have other differences and similarities that can play a role in your decision, as shown in the following table.

Qtrees	Volumes
Both enable you to organize user data. Both enable you to group users with similar needs. Both have a security style and an oplocks setting. The security style determines whether files use UNIX or Windows NT permissions. The oplocks setting determines whether files and directories use CIFS opportunistic locks. Both can be used as units in a backup and a restore. Neither can be crossed by hard links.
You can add and delete qtrees on the fly; this provides flexibility.	You can add volumes by adding disks; this makes more storage available on the filer.
You can expand and shrink qtrees.	You can expand but not shrink volumes.
You cannot create individual qtree snapshots unless you use SnapMirror. You are dependent on volume snapshots.	You can create volume snapshots, which enable you to recover and mirror data.