[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 3.5.0.26. 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?

Thanks,
  Keith

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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