Topic
7 replies Latest Post - ‏2012-12-24T16:59:43Z by The_Doctor
StefCoene
StefCoene
5 Posts
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Pinned topic AIX + SVC: number of paths

‏2012-12-21T09:17:50Z |
Hi,

We have AIX running behind 2 x VIO with NPIV and 2 SAN fabrics.
The AIX has 2 fcs devices from each VIO, so 4 fcs devices in total.
Is it supported to have each fcs zoned to 1 port on the SVC so we have 4 separated paths?
  • fcs0 to SVC node 1, port 1 (from VIO 1, connected to fabric A)
  • fcs1 to SVC node 2, port 1 (from VIO 2, connected to fabric A)
  • fcs2 to SVC node 1, port 2 (from VIO 1, connected to fabric B)
  • fcs3 to SVC node 2, port 2 (from VIO 2, connected to fabric B)

If we do so, the SVC report these as degraded.

Or is it better to only use 2 fcs devices so we don't have degraded paths on the SVC?
  • fcs0 to SVC node 1, port 1 and node 2 port 1 (from VIO 1, connected to fabric A)
  • fcs1 to SVC node 1, port 2 and node 2 port 2 (from VIO 2, connected to fabric B)
Stef
Updated on 2012-12-24T16:59:43Z at 2012-12-24T16:59:43Z by The_Doctor
  • The_Doctor
    The_Doctor
    28 Posts
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    Re: AIX + SVC: number of paths

    ‏2012-12-21T18:39:48Z  in response to StefCoene
    I believe the degradation message stems from SVC Node 1 and SVC Node 2 NOT seeing the identical WWPN (as in Part 1 of your example).

    Part 2 of your example, addresses this and would work better.... although it opens up the question of -> can your business tolerate the loss of a single HBA (or the loss of a VIOS Server) which will take out 50% of the AIX paths ?

    If so, now it's down to personal/technical preferences..... do you like 4 paths (as in your 2nd example) or 8 paths ? In practice, one could argue they both work fine. SDDPCM makes it easy to do either.

    In the absence of other info, I lean towards 2 paths from each physical HBA to an SVC or v7000. So, with 2 HBAs in each VIO Server:

    • VIO 1 has 4 paths
    • VIO 2 has 4 paths
    • AIX LPAR will still use 4 client FC adapters.... and will see 8 paths

    Examples only:

    VIO 1

    • fcs0 -> Fabric A -> SVC node 1 Port A and SVC node 2 Port A
    • fcs1 -> Fabric B -> SVC node 1 Port B and SVC node 2 Port B

    VIO 2

    • fcs0 -> Fabric A -> SVC node 1 Port C and SVC node 2 Port C
    • fcs1 -> Fabric B -> SVC node 1 Port D and SVC node 2 Port D

    AIX

    • fcs0 -> VIO 1 -> fcs0 -> Fabric A -> SVC node 1 Port A and SVC node 2 Port A
    • fcs1 -> VIO 1 -> fcs1 -> Fabric B -> SVC node 1 Port B and SVC node 2 Port B
    • fcs2 -> VIO 2 -> fcs0 -> Fabric A -> SVC node 1 Port C and SVC node 2 Port C
    • fcs3 -> VIO 2 -> fcs1 -> Fabric B -> SVC node 1 Port D and SVC node 2 Port D
    • StefCoene
      StefCoene
      5 Posts
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      Re: AIX + SVC: number of paths

      ‏2012-12-21T20:19:05Z  in response to The_Doctor
      I'm not sure if the setup with 4 separated paths is supported or not by the SVC and/or SDDPCM.

      It's also recommended to have 4 paths, so I prefer not to have 8 paths.
      I know that 8 paths is supported by the SDDPCM driver.
      So I prefer the setup 4 separated paths, even when the SVC report this as degraded.
      Stef
      • The_Doctor
        The_Doctor
        28 Posts
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        Re: AIX + SVC: number of paths

        ‏2012-12-23T17:48:58Z  in response to StefCoene
        4 or 8 paths from the NPIV enabled AIX LPAR.... the choice is yours. AFAIK, both are fully supported.

        Regarding the degradation message.....
        • is there anything specific in the message to provide a clue as the where the degradation is ?
        • are we sure the degradation message is a result of the AIX zoning ?

        Not knowing your environment, here's a few random thoughts:
        • are the VIO Servers zoned to the SVC ? i.e. are the VIOS physical WWPNs zoned to the SVC ?
        • if so:
        • - - how does this zoning look ?
        • - - maybe this zoning is the source of the degradation message.... y/n ?
        • - - is SDDPCM installed on the VIOS ?
        • and, to anticipate someone else challenging this zoning practice, yes you are correct, one does not normally zone the VIO Server physical WWPNs to anything (i.e. zoning is omitted for the physical WWPNs)..... BUT if you're booting off SAN, have alt_disk_copy volumes, or Repository volumes, or any LUN on the SAN that the VIO Servers directly access then zoning the physical WWPNs is required.
        • SystemAdmin
          SystemAdmin
          4779 Posts
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          Re: AIX + SVC: number of paths

          ‏2012-12-24T00:39:58Z  in response to The_Doctor
          Both 4 or 8 are supported, but 4 has been the preferred number of paths as there can be a performance gain by dropping down from 8 while barely sacrificing redundancy.

          I always prefer the 2 vio client NPIV adapters zoned to 4 ports total on the SVC since the other issue can be the total number of WWPNs. I couldn't find the one for 6.3 or .4, but have a look:
          http://www-01.ibm.com/support/docview.wss?uid=ssg1S1003799

          You'll notice under "Total Fibre Channel ports and iSCSI names per I/O group" that the limit is 512. This means on a 2 node SVC, the max number of hosts you can have per that iogrp is 128 if you use 4 NPIV adapters per vio client. That's also not accounting for your VIO servers doing boot from SAN or anything else in that iogrp.

          Just some food for thought...
        • StefCoene
          StefCoene
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          Re: AIX + SVC: number of paths

          ‏2012-12-24T07:17:45Z  in response to The_Doctor
          Regarding the degraded paths, I think the SVC marks the path as degraded because the WWN of the node is only logged in to 1 node.

          And regarding to the VIO, we zone the VIO also with his own WWN because we boot the VIO from the SAN. But I don't think this has anything to do with the zoning of the other lpars.

          And regarding the maximum number of fibre channels an I/O group supports, if you want to use partition mobility and you zone 4 fibre channels per host, then you use 8 WWN's per host on the SVC...
          Stef
          • SystemAdmin
            SystemAdmin
            4779 Posts
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            Re: AIX + SVC: number of paths

            ‏2012-12-24T07:23:34Z  in response to StefCoene
            The boot from SAN zoning was only mentioned because it can affect the total number of hosts per IO Group.

            If you do use 4 NPIV adapters per host, yes, LPM will require 8 WWNs per host. However, if you use 2 npiv initiators per host, LPM only requires 4 and you can stick with 4 paths per vdisk still.
          • The_Doctor
            The_Doctor
            28 Posts
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            Re: AIX + SVC: number of paths

            ‏2012-12-24T16:59:43Z  in response to StefCoene
            StefCoene wrote, in part -> And regarding to the VIO, we zone the VIO also with his own WWN because we boot the VIO from the SAN. But I don't think this has anything to do with the zoning of the other lpars.

            Correct, it doesn't. The reason for my question(s) was to understand how the physical WWPNs on each VIO were zoned, if at all. i.e. is each physical WWPN zoned to both SVC nodes or just a single node ?

            .....and from there ascertain whether or not the VIO zoning was contributing to the degradation message. e.g. is the degradation message pointing to the paths of the VIO Server(s), AIX client LPAR, or both ?

            But I think this thread has evolved beyond this question, so we'll leave it at that.