How Mirrormounts Work

The Solaris Express, Developer Edition 1/08 release includes a new mounting facility called mirrormounts. Mirrormounts allow a NFSv4 client to access files in a file system as soon as the file system is shared on an NFSv4 server. The files can be accessed without the overhead of using the mount command or updating autofs maps. In effect, once a NFSv4 file system is mounted on a client, any other file systems from that server could also be mounted.

When to Use Mirrormounts

Generally, using the mirrormount facility is optimal for your NFSv4 clients except when you:

• need to use a different hierarchy on the client, than exists on the server

• need to use different mount options than those of the parent file system

Mounting a File System Using Mirrormounts

If a file system is mounted on an NFSv4 client using manual mounts or autofs, any additional file systems added to the mounted file system, may be mounted on the client using the mirrormount facility. The client requests access to the new file system using the same mount options as were used on the parent directory. If the mount fails for any reason, the normal NFSv4 security negotiations occur between the server and the client to adjust the mount options so that the mount request succeeds.

Where there is an existing automount trigger point setup for a particular server file system, the automount trigger takes precedence over mirrormounting, so a mirrormount will not occur for that file system. To use mirrormounts in this case, the automount entry would need to be removed.

For specific instructions on how to get mirrormounts to work see:

• Using Mirrormounts After Mounting a File System

• How to Mount All File Systems from a Server

Unmounting a File System Using Mirrormounts

Mirrormounted file systems will be automatically unmounted if idle, after a certain period of inactivity. The period is set using the AUTOMOUNT_TIMEOUT property in /etc/default/autofs, which is used by the automounter for the same purpose.

If an NFS file system is manually unmounted, then any mirrormounted file systems contained within it will also be unmounted, if idle. If there is an active mirrormounted file system within, the manual unmount will fail, as though that original file system were busy. A forced unmount will, however, be propagated through to all enclosed mirror-mounted file systems.

If a file system boundary is encountered within an automounted file system, a mirrormount will occur. When the automounter unmounts the parent filesystem, any mirror-mounted file systems within it will also be automatically unmounted, if idle. If there is an active mirrormounted file system, the automatic unmount will not occur, which preserves current automount behavior.