Topic
  • 4 replies
  • Latest Post - ‏2013-01-13T13:28:20Z by SystemAdmin
SystemAdmin
SystemAdmin
2092 Posts

Pinned topic Linux nsd device type - any difference between "generic" and "dmm"

‏2013-01-02T14:54:21Z |
Hello,

I use device mapper multipath for the nsd block devices on Linux with GPFS 3.4. But I specify the nsd device type "generic" in the nsddevices script. Is there any benefit or reason why I should move to the device type "dmm" instead?

Or in other words: Does gpfs handle "dmm" devices different from "generic" devices, or is all it cares about that the type is consistent, i.e. the same, across the whole cluster for LUNs with identical names.

kind regards,

Heiner Billich
Updated on 2013-01-13T13:28:20Z at 2013-01-13T13:28:20Z by SystemAdmin
  • SystemAdmin
    SystemAdmin
    2092 Posts

    Re: Linux nsd device type - any difference between "generic" and "dmm"

    ‏2013-01-02T17:17:11Z  
    Yes, "dmm" has a special meaning to GPFS code. SCSI3 PR code keys off this disk type. More generally, you want GPFS to be able to distinguish multi-path devices from single-path ones, so you don't want to use 'generic' for both. If both types are visible to the OS (e.g. the same LUN shows up as /dev/dm-0, /dev/sdm, and /dev/sdx), using a unique device type for the MP device will allow GPFS to pick it.

    yuri
  • SystemAdmin
    SystemAdmin
    2092 Posts

    Re: Linux nsd device type - any difference between "generic" and "dmm"

    ‏2013-01-13T13:00:54Z  
    So I will switch from "generic" to "dmm" during the next maintenance - as I understand I have to unmount the affected file systems to do the change.
    Thank you,

    Heiner Billich
  • SystemAdmin
    SystemAdmin
    2092 Posts

    Re: Linux nsd device type - any difference between "generic" and "dmm"

    ‏2013-01-13T13:00:59Z  
    So I will switch from "generic" to "dmm" during the next maintenance - as I understand I have to unmount the affected file systems to do the change.
    Thank you,

    Heiner Billich
  • SystemAdmin
    SystemAdmin
    2092 Posts

    mmchconfig updateNsdType does not require to unmount

    ‏2013-01-13T13:28:20Z  
    So I will switch from "generic" to "dmm" during the next maintenance - as I understand I have to unmount the affected file systems to do the change.
    Thank you,

    Heiner Billich
    I was wrong, I could do the change without unmounting.

    1. mmchconfig updateNsdType=/tmp/filename

    nice ...