Veritas Dyanmic Multipathing

Veritas Dynamic Multipathing:

As the name indicates, veritas dynamic multipathing provides multipathing functionality for operating system native device.
It represents a multiple path of a device using DMP metadevice also known as DMP nodes .

Important points:

You can not create veritas filessytem on DMP metadevice, only way to  have the filesystem is create VxVM volume and create VxFS filesystem on it.

VxVM volume and ZFS volume can coexist together but the device which has VxVM label can not be used in ZFS and vice versa.

Feature of Multipathing:

It provides the following feature:

1. Availability
2. Reliability
3. Performance 

It does those by using path failover and load balancing.

Two kernel thread performs the checking the status of HBA and path restoration.

1. errord
2. restored

This can be checked using #vxdmpadm stat

Support for ZFS
---------------------

By default VxVM does not support zfs. To enable it, you need to turn on dmp_native_support tunable

#vxdmpadm settune dmp_native_support=on

To check the status 

#vxdmpadm gettune dmp_native_support


Here is sequence of commands to enable VxDMP support and create a zpool followed by adding a new device to the zpool.

1.Enable the dmp_native_support

#vxdmpadm settune dmp_native_support=on

2.Check the dmp_native_support status

#vxdmpadm gettune dmp_native_support

Once the above steps are done, you can go ahead and add create zpool.

3. Bring the disk under Veritas Volume manager

#vxdctl enable or #vxdisk scandisks

4. Check the disks status

#vxdisk list

5.Now its time to create zpool using the device

#zpool create testpool <device_name>

6. Check the zpool status

#zpool status

7.Add a new device

#zpool add testpool <device name>

------------------------------------------------------------------

To see all the subpaths of the dmpnode name

#vxdmpadm getsubpaths dmpnodename=<name> 

# vxdmpadm getsubpaths dmpnodename=disk_8
NAME         STATE[A]   PATH-TYPE[M] CTLR-NAME  ENCLR-TYPE   ENCLR-NAME    ATTRS
================================================================================
c2t5d0       ENABLED(A)    -          c2         Disk         disk       
      -

where disk_8 is the dmpnodename

Now the next is when we have device details, wants to find out the corresponding dmpnodename


# vxdmpadm getdmpnode nodename=c2t5d0
NAME                 STATE        ENCLR-TYPE   PATHS  ENBL  DSBL  ENCLR-NAME
==============================================================================
disk_8  

Others useful commands

#vxdmpadm list dmpnode all

#vxdmpadm list dmpnode dmpnodename=<dmp node name>

# vxdmpadm list dmpnode dmpnodename=disk_4
dmpdev          = disk_4
state           = enabled
enclosure       = disk
cab-sno         = DISKS
asl             = scsi3_jbod
vid             = VMware,
pid             = VMware Virtual S
array-name      = Disk
array-type      = Disk
iopolicy        = MinimumQ
avid            = -
lun-sno         = 6000C29A8511F1C593A6B3235534E5EA
udid            = VMware%2C%5FVMware%20Virtual%20S%5FDISKS%5F6000C29A8511F1C593A6B3235534E5EA
dev-attr        = -
###path         = name state type transport ctlr hwpath aportID aportWWN attr
path            = c2t1d0s2 enabled(a) - SCSI c2 /pci@0,0/pci15ad,1976@10 - - -
#