[gpfsug-discuss] restripe or not

Bob Oesterlin oester at gmail.com
Tue Nov 25 02:01:06 GMT 2014

In general, the need to restripe after a disk add is dependent on a number
of factors, as has been pointed out.. A couple of other

- One thing you might consider (depending on your pattern of read/write
traffic), is selectively suspending one or more of the existing NSDs,
forcing GPFS to write new blocks to the new NSDs. That way at least some of
the new data is being written to the new storage by default, rather than
using up blocks on the existing NSDs. You can suspend/resume disks at any

- You can pick a subset of nodes to perform the restripe with "mmrestripefs
-N node1,node2,..." Keep in mind you'll get much better performance and
less impact to the filesystem if you choose NSD servers with direct access
to the disk.

- Resume of restripe: Yes, you can do this, no harm, done it many times.
You can track the balance of the disks using "mmdf <filesystem>". This is a
pretty intensive command, so I wouldn't run in frequently. Check it a few
times each day, see if the data balance is improving by itself. When you
stop/restart it, the restripe doesn't pick up exactly where it left off,
it's going to scan the entire file system again.

- You can also restripe single files if the are large and get a heavy I/O

Bob Oesterlin
Nuance Communications

On Mon, Nov 24, 2014 at 3:22 PM, Stijn De Weirdt <stijn.deweirdt at ugent.be>

> hi all,
> we are going to expand an existing filestytem with approx 50% capacity.
> the current filesystem is 75% full.
> we are in downtime (for more then just this reason), so we can take the IO
> rebalance hit for a while (say max 48hours).
> my questions:
> a. do we really need to rebalance? the mmadddisk page suggest normally
> it's going to be ok, but i never understood that. new data will end up
> mainly on new disks, so wrt to performance, this can't really work out, can
> it?
> b. can we change the priority of rebalancing somehow (fewer nodes taking
> part in the rebalance?)
> c. once we start the rebalance, how save is it to stop with kill or ctrl-c
> (or can we say eg. rebalance 25% now, rest later?)
> (and how often can we do this? eg a daily cron job to restripe at max one
> hour per day, would this cause issue in the long term
> many thanks,
> stijn
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