[gpfsug-discuss] How to shrink GPFS on DSSG's?

IBM Spectrum Scale scale at us.ibm.com
Tue Jul 19 19:21:47 BST 2022

Adding Steve and Wes to provide guidance on ESS commands.

Regards, The Spectrum Scale (GPFS) team


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From:	"Peter Childs" <p.childs at qmul.ac.uk>
To:	"gpfsug-discuss at spectrumscale.org"
            <gpfsug-discuss at spectrumscale.org>
Date:	22-06-2022 03.36 PM
Subject:	Re: [gpfsug-discuss] [EXTERNAL]  How to shrink GPFS on DSSG's?
Sent by:	"gpfsug-discuss" <gpfsug-discuss-bounces at gpfsug.org>

Having only just got an ESS I'm still learning how GNR works. as I read it
there are currently two "breeds" of GNR, the version on the "DSS and ESS
appliances" and the one in "Erasure Code Edition"

As I understand it from past talks using mmdeldisk to remove a disk works
fine in none GNR editions but is not the best way to do the task.

My understanding is that you should

mmchdisk suspend/empty # so new data is not put on the disk but the disk
remains available for read.
mmrestripefs -m # to move the data off the disk
mmdeldisk # to actually remove the disk which should be fast as its already
been emptied.

We have done this with success in the past to migrate data between Raid6
arrays, with success.

I believe there are some commands with mmvdisk to re-shape recovery groups
in GNR but I've not as yet worked out how they work.

Peter Childs

From: gpfsug-discuss <gpfsug-discuss-bounces at gpfsug.org> on behalf of Jaime
Pinto <pinto at scinet.utoronto.ca>
Sent: Monday, June 20, 2022 7:04 PM
To: gpfsug-discuss at spectrumscale.org
Subject: [EXTERNAL] [gpfsug-discuss] How to shrink GPFS on DSSG's?

CAUTION: This email originated from outside of QMUL. Do not click links or
open attachments unless you recognise the sender and know the content is

I'm wondering if it's possible to shrink GPFS gracefully. I've seen some
references to that effect on some presentations, however I can't find
detailed instructions on any formal IBM documentation on how to do it.

About 3 years ago we launched a new GPFS deployment with 3 DSS-G enclosures
(9.6PB usable).
Some 1.5 years later we added 2 more enclosures, for a total of 16PB, and
only 7PB occupancy so far.

Basically I'd like to return to the original 3 enclosures, and still
maintain the (8+2p) parity level.

Any suggestions?

Jaime Pinto - Storage Analyst
SciNet HPC Consortium - www.scinet.utoronto.ca
University of Toronto

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