[LU-17335] allow "lctl barrier_freeze" to exclude MGS target

• Type: Improvement
• Resolution: Unresolved
• Priority: Major
• Affects Version/s: Lustre 2.16.0
• Severity: 3
• Assignee: Emoly Liu
• Reporter: Andreas Dilger

Description

For doing storage system configuration changes (e.g. adding new MDTs and OSTs to the filesystem) it is desirable to allow blocking modifications to the filesystem using the "lctl barrier_freeze" command. However, this also freezes the MGT device, preventing new MDT and OST devices from registering themselves with the MGS.

It would be desirable to have an option like "lctl barrier_freeze --nomgs" (similar to the "nomgs" option for mkfs.lustre and mount.lustre) to freeze all of the storage targets (MDT, OST) but exclude the MGT device. Currently, if barrier_freeze is used the MDT/OST addition fails with the following error on the MGS:

Lustre: MGS: the system is in barrier, refuse the connection from MDT es01a-MDT0007 temporary

and the following on the MDS server:

LustreError: 15f-b: es01a-MDT0007: cannot register this server with the MGS: rc = -16. Is the MGS running?
LustreError: 41629:0:(obd_mount_server.c:2061:server_fill_super()) Unable to start targets: -16
LustreError: 41629:0:(obd_mount_server.c:1641:server_put_super()) no obd es01a-MDT0007
LustreError: 41629:0:(obd_mount_server.c:133:server_deregister_mount()) es01a-MDT0007 not registered
Lustre: server umount es01a-MDT0007 complete

For testing, this could use a modified version of test_46b in patch https://review.whamcloud.com/53300 that adds an "lctl barrier_freeze --nomgs ..." command before the new MDT/OST devices are added to the filesystem, and then un-freezes the filesystem after the OSTs appear on the client (e.g. in "lfs df").