[gpfsug-discuss] Control of where mmcrsnapshot runs?

Keith Ball bipcuds at gmail.com
Thu Mar 29 17:15:19 BST 2018

You're right, Brian, the key load will be on the filesystem manager in any
case, and as you say, all nodes nodes must quiesce - it's not really an
issue of where to run the command, like it would be for mmfsck, etc.

GPFS version is We'll investigate upgrade to later version that
accommodates combined operations.

I will also look into the cgroups approach - is this a documented thing, or
just something that people have tinkered with/hand rolled?


On Wed, Mar 28, 2018 at 7:00 AM, <gpfsug-discuss-
<gpfsug-discuss-request at spectrumscale.org>

> What version of GPFS are you running Keith?
> All nodes mounting the file system must briefly quiesce I/O operations
> during the snapshot create operations, hence the ?Quiescing all file system
> operations.? message in the output.  So don?t really see a way to specify a
> specific set of nodes for these operations.  They have made updates in
> newer releases of GPFS to combine operations (e.g. create and delete
> snapshots at the same time) which IBM says ?system performance is increased
> by batching operations and reducing overhead.?.
> Trying to isolate GPFS resources (e.g. cgroups) on the clients (e.g. CPU
> and memory resources dedicated to GPFS/SSH/kernel/networking/etc) can
> help them respond more quickly to quiesce I/O requests.
> HTH,
> -Bryan
> From: gpfsug-discuss-bounces at spectrumscale.org [mailto:gpfsug-discuss-
> bounces at spectrumscale.org] On Behalf Of Keith Ball
> Sent: Tuesday, March 27, 2018 5:26 PM
> To: gpfsug-discuss at spectrumscale.org
> Subject: [gpfsug-discuss] Control of where mmcrsnapshot runs?
> Note: External Email
> ________________________________
> Hi All,
> Two questions on snapshots:
> 1.) I note that neither "mmcrsnapshot" nor "mmdelsnapshot" appear to have
> an "-N" option as "PIT" commands typically do. Is there any way to control
> where threads for snapshot creation/deletion run? (I assume the filesystem
> manager will always be involved regardless).
> 2.) When mmdelsnapshot hangs or times out, the error messages tend to
> appear on client nodes, and not necessarily the node where mmdelsnapshot is
> run from, not the FS manager. Besides telling all users "don't use any I/O"
> when runnign these commands, are there ways that folks have found to avoid
> hangs and timeouts of mmdelsnapshot?
> FWIW our filesystem manager is probably overextended (replication factor 2
> on data+MD, 30 daily snapshots kept, a number of client clusters served,
> plus the FS manager is also an NSD server).
> Many Thanks,
>   Keith
> RedLine Performance Solutions LLC
> ________________________________
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