[gpfsug-discuss] Mass UID migration suggestions

[hpc-luke at uconn.edu]

Hello, 

	We're trying to change most of our users uids, is there a clean way to
migrate all of one users files with say `mmapplypolicy`? We have to change the
owner of around 273539588 files, and my estimates for runtime are around 6 days.

	What we've been doing is indexing all of the files and splitting them up by
owner which takes around an hour, and then we were locking the user out while we
chown their files. I made it multi threaded as it weirdly gave a 10% speedup
despite my expectation that multi threading access from a single node would not
give any speedup.

	Generally I'm looking for advice on how to make the chowning faster. Would
spreading the chowning processes over multiple nodes improve performance? Should
I not stat the files before running lchown on them, since lchown checks the file
before changing it? I saw mention of inodescan(), in an old gpfsug email, which
speeds up disk read access, by not guaranteeing that the data is up to date. We
have a maintenance day coming up where all users will be locked out, so the file
handles(?) from GPFS's perspective will not be able to go stale. Is there a
function with similar constraints to inodescan that I can use to speed up this
process?

Thank you for your time,

Luke
Storrs-HPC
University of Connecticut