[gpfsug-discuss] Question about NSD "Devtype" setting, nsddevices file

Eric Ross er.a.ross at gmail.com
Thu Jan 18 20:22:09 GMT 2018


I would say that's what it *appears* to be doing.  The sys admin in me
would still want some "official" word from IBM, as I wouldn't my
assumption to be the cause of a meltdown at 16.50 on a Friday when
everyone is heading out for the weekend ;)

Cheers,
-Eric

On Thu, Jan 18, 2018 at 2:09 PM, Bryan Banister
<bbanister at jumptrading.com> wrote:
> Great!  So this is just for selecting devices and according to my `mmlsnsd -X` output it's using the correct ones, so I can probably return to ignoring this parameter!
> -Bryan
>
> -----Original Message-----
> From: gpfsug-discuss-bounces at spectrumscale.org [mailto:gpfsug-discuss-bounces at spectrumscale.org] On Behalf Of Eric Ross
> Sent: Thursday, January 18, 2018 2:01 PM
> To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
> Subject: Re: [gpfsug-discuss] Question about NSD "Devtype" setting, nsddevices file
>
> Note: External Email
> -------------------------------------------------
>
> Bryan,
>
> While waiting on the "official" word as to what each setting does
> differently,  I remembered there was a brief explanation of the
> differences (at least of dmm vs generic) in the
> /var/mmfs/etc/nsddevices included with the GPFS-goodies toolkit
> (https://github.com/finley/GPFS-Goodies) I use to use when I was at
> IBM.
>
> //snip
>
> dmm vs. generic is used by GPFS to prioritize internal order of
> searching through available disks, then later GPFS discards other
> disk device names that it finds that match as the same NSD device
> by a different path.  For this reason, dmm vs. generic is an
> important distinction if you are not explicitly producing the
> entire and exclusive set of disks that GPFS should use, as output
> from this script (nsddevices) _and_ exiting this script with a
> "return 0". -Brian Finley
>
> //end snip
>
> If I read that correctly, it would indicate GPFS uses those additional
> labels (at least dmm vs generic) as a mechanism to determine which
> device files to prefer when scanning a system and finding the same NSD
> available via different devices (i.e. /dev/mapper/foo vs
> /dev/sdq,/dev/sdx).  By associating dmm with the dm-multipathed
> device, I guess it would just ignore the /dev/sd${foo} devices when it
> scans them.  Also, the difference only seems to matter if you're not
> explicitly creating a list a Brian F. indicates.  If you simply
> generate the list and exit (via return 0), GPFS wouldn't continue
> scanning, and then find the associated /dev/sd${foo} devices to begin
> with, and therefore wouldn't need a label like dmm to prioritize it
> over say a generic device.
>
>
> - Eric
>
> On Thu, Jan 18, 2018 at 10:59 AM, Bryan Banister
> <bbanister at jumptrading.com> wrote:
>> Yes, just change the /var/mmfs/etc/nsddevices file so that it sets the
>> Devtype to the “correct” setting, for example:
>>
>>
>>
>> if [[ $osName = Linux ]]
>>
>> then
>>
>>   : # Add function to discover disks in the Linux environment.
>>
>>   ls -l /dev/mpath/ 2>/dev/null | awk '{print "mpath/"$9 " generic"}'
>>
>>   ls -l /dev/mapper/ 2>/dev/null | awk '{print "mapper/"$9 " dmm"}'
>>
>>   ls -1 /dev/vd* 2>/dev/null | awk -F '/' '{print ""$3 " generic"}'
>>
>> fi
>>
>>
>>
>> My question is what is the correct setting?
>>
>>
>>
>> And what does GPFS do differently with each setting?
>>
>>
>>
>> Thanks,
>>
>> -Bryan
>>
>>
>>
>> From: gpfsug-discuss-bounces at spectrumscale.org
>> [mailto:gpfsug-discuss-bounces at spectrumscale.org] On Behalf Of Jeffrey R.
>> Lang
>> Sent: Thursday, January 18, 2018 9:20 AM
>> To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
>> Subject: Re: [gpfsug-discuss] Question about NSD "Devtype" setting,
>> nsddevices file
>>
>>
>>
>> Note: External Email
>>
>> ________________________________
>>
>> So is there a way to change it if it’s set incorrectly?
>>
>>
>>
>> jeff
>>
>>
>>
>> From: gpfsug-discuss-bounces at spectrumscale.org
>> [mailto:gpfsug-discuss-bounces at spectrumscale.org] On Behalf Of Jim Doherty
>> Sent: Wednesday, January 17, 2018 6:28 PM
>> To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
>> Subject: Re: [gpfsug-discuss] Question about NSD "Devtype" setting,
>> nsddevices file
>>
>>
>>
>>
>>
>> Run a mmlsnsd -X   I suspect you will see that GPFS is using one of the
>> /dev/sd* "generic" paths to the LUN,   not the /dev/mapper/ path.   In our
>> case the device is setup as dmm
>>
>>
>>
>> [root at service5 ~]# mmlsnsd -X
>>
>>  Disk name    NSD volume ID      Device         Devtype  Node name
>> Remarks
>> ---------------------------------------------------------------------------------------------------
>>  volume1      0972B6CD587CD8E0   /dev/dm-0      dmm
>> service5.pok.stglabs.ibm.com server node
>>  volume1      0972B6CD587CD8E0   /dev/dm-0      dmm
>> service6.pok.stglabs.ibm.com server node
>>  volume2      0972B6CE587CD8E4   /dev/dm-4      dmm
>> service5.pok.stglabs.ibm.com server node
>>  volume2      0972B6CE587CD8E4   /dev/dm-3      dmm
>> service6.pok.stglabs.ibm.com server node
>>  volume3      0972B6CD587CD8E7   /dev/dm-1      dmm
>> service5.pok.stglabs.ibm.com server node
>>  volume3      0972B6CD587CD8E7   /dev/dm-2      dmm
>> service6.pok.stglabs.ibm.com server node
>>  volume4      0972B6CE587CF625   /dev/dm-3      dmm
>> service5.pok.stglabs.ibm.com server node
>>  volume4      0972B6CE587CF625   /dev/dm-4      dmm
>> service6.pok.stglabs.ibm.com server node
>>
>> [root at service5 ~]# grep volume1 /var/mmfs/gen/mmsdrfs | grep SG_DISK
>> %%home%%:60_SG_DISKS:gpfs5:1:volume1:0:5001:dataAndMetadata:0972B6CD587CD8E0:nsd:service5.pok.stglabs.ibm.com,service6.pok.stglabs.ibm.com::other::dmm:user:::quorumDisk:ready::system:service5.pok.stglabs.ibm.com,service6.pok.stglabs.ibm.com:::::
>> [root at service5 ~]#
>>
>>
>>
>> If you run an tspreparedisk -s  it will show you all of the paths.
>>
>>
>>
>> [root at service5 ~]# tspreparedisk -s | grep 0972B6CD587CD8E0
>> 0972B6CD587CD8E0 /dev/sda generic
>> 0972B6CD587CD8E0 /dev/sdk generic
>> 0972B6CD587CD8E0 /dev/sdu generic
>> 0972B6CD587CD8E0 /dev/sdah generic
>> 0972B6CD587CD8E0 /dev/dm-0 dmm
>> [root at service5 ~]#
>>
>>
>>
>> Jim
>>
>>
>>
>>
>>
>>
>>
>> Jim
>>
>> On Wednesday, January 17, 2018, 5:12:10 PM EST, Bryan Banister
>> <bbanister at jumptrading.com> wrote:
>>
>>
>>
>>
>>
>> Hi all,
>>
>>
>>
>> We are reviewing some of our configurations and were not sure what to make
>> of the NSD Device Types that GPFS uses and what, if anything, do they change
>> about how GPFS accesses/recovers/manages/etc the underlying storage based on
>> this setting.
>>
>>
>>
>> The documentation doesn’t say much about it other than to consult the
>> /usr/lpp/mmfs/bin/mmdevdiscover command (no man page), which has this
>> section:
>>
>>
>>
>> # Known disk types currently are:
>>
>> #
>>
>> #   powerdisk  - EMC power path disk
>>
>> #   vpath      - IBM virtual path disk
>>
>> #   dmm        - Device-Mapper Multipath (DMM)
>>
>> #   dlmfdrv    - Hitachi dlm
>>
>> #   hdisk      - AIX hard disk
>>
>> #   lv         - AIX logical volume.  Historical usage only.
>>
>> #                Not allowed as a new device to mmcrnsd.
>>
>> #   gpt        - GPFS partition on Windows disk
>>
>> #   generic    - Device having no unique failover or multipathing
>>
>> #                characteristic (predominantly Linux devices).
>>
>> #   dasd       - DASD device (for Linux on z Systems)
>>
>>
>>
>> We have our storage under Linux Device-Mapper Multipath control (two device
>> paths to all storage, active/passive) and are accessible under /dev/mapper,
>> but the NSD types are current set to ‘generic’ not ‘dmm’.  This is
>> configured in the /var/mmfs/etc/nsddevices file:
>>
>>
>>
>> if [[ $osName = Linux ]]
>>
>> then
>>
>>   : # Add function to discover disks in the Linux environment.
>>
>>   ls -l /dev/mpath/ 2>/dev/null | awk '{print "mpath/"$9 " generic"}'
>>
>>   ls -l /dev/mapper/ 2>/dev/null | awk '{print "mapper/"$9 " generic"}'
>>
>>   ls -1 /dev/vd* 2>/dev/null | awk -F '/' '{print ""$3 " generic"}'
>>
>> fi
>>
>>
>>
>> Can somebody from IBM explain what the correct setting should be and what
>> differences GPFS does with ‘generic’ vs. ‘dmm’ vs. others?
>>
>>
>>
>> Thanks in advance!
>>
>> -Bryan
>>
>>
>>
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