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VXVM Tutorial 7- VXDMP(Dynamic Multi Pathing)

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               VXVM(veritas volume manager training) 7 of 10
Veritas Dynamic Multi-Pathing provides greater availability, reliability to SAN paths and it increase the SAN I/O using load balancing .SAN path redundancy ensured by path failover.


What is multi-pathing software ?
Server is connected to SAN using one or more fiber channel(FC) in different controllers.But without multi-pathing software the UNIX operating system incorrectly interprets the two path as leading to two storage units(LUN). By using multi pathing software,tow paths as leading to the same storage unit.(LUN)

Unix Multi-pathing software importance


How VxDMP works ?

VXDMP Represents multi-paths to a LUN in SAN environments
                                                        Thanks to www.symantec.com

In the above diagram,LUN is created with name of enc0 and depending on the path, LUN can be accessed by using c1t99d0 or c2t99d0.But vxdmp sees c1t99d0 & c2t99d0 as single SAN unit. If we loose c1 (controller) still we can access the LUN via c2t99d0.


VX-DMP supports the following support arrays:

  • Active/Active (A/A)
  • Asymmetric Active/Active (A/A-A)
  • Asymmetric Logical Unit Access(ALUA)
  • Active/Passive (A/P)
  • Active/Passive in explicit failover mode or non-autotrespass mode (A/P-F)
  • Active/Passive withLUNgroup failover (A/P-G)
DISPLAYING VXDMP INFORMATION:

To list the controllers,
# vxdmpadm listctlr all
CTLR-NAME       ENCLR-TYPE      STATE      ENCLR-NAME
=====================================================
c2              EMC             ENABLED      emc0
c4              EMC             ENABLED      emc0
c0              Disk            ENABLED      disk
c1              Disk            ENABLED      disk

As per the above output,we have two controllers for emc0 enclosure.


To list the enclosures,

# vxdmpadm listenclosure all
ENCLR_NAME ENCLR_TYPE  ENCLR_SNO  STATUS ARRAY_TYPE LUN_COUNT
==============================================================
emc0         EMC     000292704216 CONNECTED    A/A    331
disk         Disk    DISKS        CONNECTED    Disk   4
Here you can see ,we have two enclosure are available. emc0 (SAN) & disk(local disks)


To find what are Disk are using controller c1,
bash-3.00# vxdmpadm getsubpaths ctlr=c1
NAME STATE[A] PATH-TYPE[M] DMPNODENAME ENCLR-TYPE ENCLR-NAMEATTRS
======================================================
c1t3d0 ENABLED(A)    -      disk_0     Disk     disk           -
c1t5d0 ENABLED(A)    -      disk_1     Disk     disk           -
c1t4d0 ENABLED(A)    -      disk_2     Disk     disk           -

To see specific LUN multi-paths,
# vxdmpadm getsubpaths dmpnodename=emc0_0e790
NAME   STATE[A] PATH-TYPE[M] CTLR-NAME ENCLR-TYPE ENCLR-NAMEATTRS
=================================================================
c2t3000034578233D18d57s2 ENABLED(A)   -  c2   EMC   emc0    -
c4t3000034578233D24d57s2 ENABLED(A)   -  c4   EMC   emc0    -

To find who controls the path,i.e to find the enclosure based name.
# vxdmpadm getdmpnode nodename=c2t3000034578233D18d57s2
NAME        STATE   ENCLR-TYPE PATHS  ENBL  DSBL  ENCLR-NAME
================================================================
emc0_0e790 ENABLED    EMC        2      4     0     emc0

To see what are the disks are coming from emc0 enclosure,
# vxdmpadm getdmpnode enclosure=emc0
NAME        STATE     ENCLR-TYPE   PATHS  ENBL  DSBL  ENCLR-NAME
===============================================================
emc0_0e790  ENABLED      EMC          2      4     0     emc0

To disable controller,
# vxdmpadm listctlr all
CTLR-NAME       ENCLR-TYPE      STATE      ENCLR-NAME
===========================================================
c1              Disk            ENABLED      disk
c2              EMC             ENABLED      emc0
c4              EMC             ENABLED      emc0
# vxdmpadm disable ctlr=c2

# vxdmpadm listctlr all

CTLR-NAME       ENCLR-TYPE      STATE      ENCLR-NAME
===========================================================
c1              Disk            ENABLED       disk
c2              EMC             DISABLED      emc0
c4              EMC             ENABLED       emc0

To enable controller,

# vxdmpadm enable ctlr=c2

# vxdmpadm listctlr all
CTLR-NAME       ENCLR-TYPE      STATE      ENCLR-NAME
===========================================================
c1              Disk            ENABLED      disk
c2              EMC             ENABLED      emc0
c4              EMC             ENABLED      emc0
VXDMP I/O statistics:

# vxdmpadm iostat show all

VxVM vxdmpadm ERROR V-5-1-14678 DMP IO Statistics collection activity has been stopped. Use ‘vxdmpadm iostat start’ to restart IO Statistics collection and try again.

To start the statistics collection,

# vxdmpadm iostat start

To see the statistics,
# vxdmpadm iostat show all
            cpu usage = 10883us    per cpu memory = 28672b
             OPERATIONS            BLOCKS          AVG TIME(ms)
PATHNAME   READS    WRITES     READS    WRITES     READS   WRITES
c1t0d0s2    13         0       221         0   20.51     0.00
c1t1d0      381      2396    207193    704884   24.01    16.28
c1t2d0      361      2567    207034    766221   15.02    20.96
c1t3d0     46792      9806   1336359    804680    1.10    16.68

You can reset the statistics to being the monitoring,

# vxdmpadm iostat reset
# vxdmpadm iostat show all
            cpu usage = 1us    per cpu memory = 28672b
           OPERATIONS            BLOCKS          AVG TIME(ms)
PATHNAME    READS    WRITES     READS    WRITES     READS  WRITES
c1t0d0s2      0         0         0         0    0.00     0.00
c1t1d0        0         0         0         0    0.00     0.00
c1t2d0        0         0         0         0    0.00     0.00
c1t3d0        0         0         0         0    0.00     0.00
I/O policy (I/O load balancing):

To get the enclosure names,
bash-3.00# vxdmpadm listenclosure all
ENCLR_NAME ENCLR_TYPE ENCLR_SNO  STATUS  ARRAY_TYPE     LUN_COUNT
=================================================================
disk       Disk       DISKS      CONNECTED    Disk        7
To get the current I/O Policy for ensloure,
bash-3.00# vxdmpadm getattr enclosure disk iopolicy
ENCLR_NAME     DEFAULT        CURRENT
=========================================================
disk           MinimumQ       MinimumQ
To modify the I/O policy for the enclosure,
bash-3.00# vxdmpadm setattr enclosure disk iopolicy=balanced
bash-3.00# vxdmpadm getattr enclosure disk iopolicy
ENCLR_NAME     DEFAULT        CURRENT
=========================================================
disk           MinimumQ       Balanced

FYI: iopolicy can be either:

  •  adaptive
  •  adaptiveminq
  •  balanced
  •  minimumq
  •  priority
  •  round-robin
  •  singleactive

To stop DMP,

# vxdmpadm stop restore


To start DMP,

# vxdmpadm start restore


If its already running , you will get below warning messages.
# vxdmpadm start restore
VxVM vxdmpadm ERROR V-5-1-3243  The VxVM restore daemon is already running. You can stop and restart the restore daemon with desired arguments for changing any of its parameters.

Thank you for reading this. If you have any doubt,Please leave a comment and i will get back to you as soon as possible.

Reader Interactions

Comments

  1. rajesh says

    Hi,

    Please tell me the step by step procedure to remove lun from the server…..?

    Also what is dm-name means….?

    Regards,
    Rajesh

    Reply

  2. Midgard says

    Hello. Thank you for this article.
    I have one question. I have a hba port failure (format says disk failure for all c2 disks, also luxadm and fcinfo. into VX conf I have c2 and c3 enabled, when I do vxdisk list I got all disk starting with c2*. I have to migrate c2 to c5, and i think it must be done by typing
    vxdmpadm enable path=c5
    vxdmpadm disable path=c2

    But not sure what will happen after that, my vxdisk list is showing c2, is it will siwitch to c3 automatically? And am I missing some commands to clean all c2 paths and add new c5? is it a online change?

    Thanks in advance, I hope you can bring some light here.

    Reply

    • Lingeswaran R says

      By default, your alternate path will get active if you have done the zoning properly. If you want to completely remove C2 , you need to perform the VXVM device tree clean up. or you can exclude the c2 controller completely.

      Regards
      Lingesh

      Reply

    • Lingeswaran R says

      i know its too late….but still registering my comment …..

      Use vxdctl enable or vxconfigd -k commands to detect the new path forcefully.

      FYI- New path will be detected automatically by vxvm .(it scans the path periodically.YOu may need to wait a bit. 5~mins )

      Lingesh

      Reply

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