[gpfsug-discuss] mmchdisk suspend / stop

[Sobey, Richard A]

Sorry I can’t help… the only thing going round and round my head right now is why on earth the existing controller cannot push the required firmware to the new one when it comes online. Never heard of anything else! Feel free to name and shame so I can avoid 😊

Richard

From: gpfsug-discuss-bounces at spectrumscale.org [mailto:gpfsug-discuss-bounces at spectrumscale.org] On Behalf Of Buterbaugh, Kevin L
Sent: 08 February 2018 16:00
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Subject: [gpfsug-discuss] mmchdisk suspend / stop

Hi All,

We are in a bit of a difficult situation right now with one of our non-IBM hardware vendors (I know, I know, I KNOW - buy IBM hardware! <grin>) and are looking for some advice on how to deal with this unfortunate situation.

We have a non-IBM FC storage array with dual-“redundant” controllers.  One of those controllers is dead and the vendor is sending us a replacement.  However, the replacement controller will have mis-matched firmware with the surviving controller and - long story short - the vendor says there is no way to resolve that without taking the storage array down for firmware upgrades.  Needless to say there’s more to that story than what I’ve included here, but I won’t bore everyone with unnecessary details.

The storage array has 5 NSDs on it, but fortunately enough they are part of our “capacity” pool … i.e. the only way a file lands here is if an mmapplypolicy scan moved it there because the *access* time is greater than 90 days.  Filesystem data replication is set to one.

So … what I was wondering if I could do is to use mmchdisk to either suspend or (preferably) stop those NSDs, do the firmware upgrade, and resume the NSDs?  The problem I see is that suspend doesn’t stop I/O, it only prevents the allocation of new blocks … so, in theory, if a user suddenly decided to start using a file they hadn’t needed for 3 months then I’ve got a problem.  Stopping all I/O to the disks is what I really want to do.  However, according to the mmchdisk man page stop cannot be used on a filesystem with replication set to one.

There’s over 250 TB of data on those 5 NSDs, so restriping off of them or setting replication to two are not options.

It is very unlikely that anyone would try to access a file on those NSDs during the hour or so I’d need to do the firmware upgrades, but how would GPFS itself react to those (suspended) disks going away for a while?  I’m thinking I could be OK if there was just a way to actually stop them rather than suspend them.  Any undocumented options to mmchdisk that I’m not aware of???

Are there other options - besides buying IBM hardware - that I am overlooking?  Thanks...
—
Kevin Buterbaugh - Senior System Administrator
Vanderbilt University - Advanced Computing Center for Research and Education
Kevin.Buterbaugh at vanderbilt.edu<mailto:Kevin.Buterbaugh at vanderbilt.edu> - (615)875-9633



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