[LU-13078] mgs trigger umount of clients

• Type: New Feature
• Resolution: Unresolved
• Priority: Minor
• Assignee: Peter Jones
• Reporter: Mahmoud Hanafi

Description

It would a great feature for the MGS to ask/force a client to umount. This can be very useful in very large clusters with multiple networks.

Issue Links

• duplicates: LU-5703 Quiesce client mountpoints from the server
• is related to: LU-17217 Allow server to control/deny client connections

Comments

[Andreas Dilger]

Attached the ancient controlled-server-shutdown.diff patch from bugzilla 18496. It will be hopelessly outdated, but may be a starting point for a new implementation.

Newer kernels have the concept of a forced "abort/shutdown" of a mountpoint, which is a hard stop in case of corruption (e.g. ext4_abort()). We already have this to some extent in Lustre with ESHUTDOWN, but there is no way to trigger this manually.

[Andreas Dilger]

One difference in this request vs. Simplified Interoperability is that unmounting a client may be problematic due to open file handles, unlike the original proposal which only quiescent the client mountpoints. The VFS will prevent the unmount with open files due to reference counting on the filesystem mountpoint. In newer kernels it may be possible to abort/evict the file handles from the filesystem side, but this would cause application errors.

[Andreas Dilger]

This is similar to a feature which has been discussed in the past under the name of "Simplified Interoperability". In that feature the intent is to quiesce clients during a server failover or upgrade. There is already an architecture document for this feature, and surprisingly an old patch in the bugzilla 18496 ticket as well, though it is against Lustre 2.0 and would obviously need to be updated, but may at least serve as a guide for implementation.