Understanding qtree creation

When to create qtrees

You create qtrees when you want to group files without creating a volume. You can group files by any combination of the following criteria:

Security style
Oplocks setting
Quota limit
Backup unit

Using qtrees for projects

One way to group files is to set up a qtree for a project, such as one maintaining a database. Setting up a qtree for a project enables you to do the following actions:

Set the security style of the project without affecting the security style of other projects.
For example, you use NTFS-style security if the members of the project use Windows files and applications. Another project in another qtree can use UNIX files and applications, and yet another project can use Windows as well as UNIX files.
If the project uses Windows, set CIFS oplocks (opportunistic locks) as appropriate to the project, without affecting other projects.
For example, if one project uses a database that requires no CIFS oplocks, you can set CIFS oplocks to Off on that project qtree. If another project uses CIFS oplocks, it can be in another qtree that has oplocks set to On.
Use quotas to limit the disk space and number of files available to a project qtree so that the project does not use up resources that other projects and users need. For instructions about managing disk space by using quotas, see Chapter 8, Disk Space Management Using Quotas.
Back up and restore all the project files as a unit.

Using qtrees for backups

You can back up individual qtrees to

Add flexibility to backup schedules
Modularize backups by backing up only one set of qtrees at a time
Keep the size of each backup to one tape

Qtree limitations

Qtrees have the following limitations:

There is a limit of 254 qtrees per volume.
When you enter a df command on a UNIX client with a path name of a qtree, the command shows the smaller of the client's file system limit or the filer disk space. This makes the qtree look fuller than it is. For additional information, see Ascertaining free disk space.

Detailed information

Creating a qtree involves the activities described in the following topics:

If you do not want to accept the default security style of a volume or a qtree, you can change it, as described in Changing the security style of a volume or a qtree.

If you do not want to accept the default CIFS oplocks setting of a volume or a qtree, you can change it, as described in Changing the CIFS oplocks setting.