[lustre-discuss] Making a file system read-only

[Cameron Harr]

Greetings,

I'll be retiring a 2.5 ZFS-backed file system in the coming months and 
plan on putting it in a "read-only" state for 6 weeks or so to let users 
archive or migrate data they want. The optimal, if slightly 
contradictory, definition of "read-only" for me would be to allow 
unlinks, but disallow all other writes; however, if that's not possible, 
then disallowing all writes would be sufficient. I will be doing some 
testing, but our 2.5 T&D system won't be available for several days and 
am therefore soliciting advice up front.

Option 1 is to remount the file system on the clients in read-only mode, 
but I can imagine a couple problems with this method.

Option 2 is to deactivate the OSTs with lctl, but that also leaves me 
with some questions. In section 14.8.3.1a of the Lustre manual, it 
recommends setting max_create_count=0 with Lustre 2.9 and above. I'm 
using 2.5, not 2.9, but noticed that 
/proc/fs/lustre/osp/fs-*-osc-MDT0000/max_create_count does indeed exist. 
Does setting that option in 2.5 still have an effect in prohibiting new 
file and directory creates? Additionally, will clients be OK having all 
OSTs inactive?

Is there another viable option?

Many thanks,
Cameron