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show me double entry for each storage point

 
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Viney Kumar
Regular Advisor

show me double entry for each storage point

Hi


When i check ioscan -fnC disk output. It show me double entry for each storage point. why and what is the purpose of it. we using lun points from SYMMETRIX.
5 REPLIES 5
Hasan  Atasoy
Honored Contributor

Re: show me double entry for each storage point

if you are using 11.23 or prevous version of hp-ux you will see one device addres for each path of the disk. in your case you have 2 path for each device. you can use pvlinks or powerpath ( emc software ) for multipathing. if you use 11.31 ( 11iv3 ) version of hpux . it supports native multipathing and in the new device naming you ill see one device name for each physical disk.

Hasan
sujit kumar singh
Honored Contributor
Solution

Re: show me double entry for each storage point

hello


what can be noted that they are showing the different Hardware paths and that they are also showing the different device files for the same LUN.

these are actually the different hardware paths to the same LUN and they can be configured as the Alternate Links for the PVs in the VG using vgextend. after set as the Alternate Link they can gove the path redundancy for that PV in the VG in case of the Priamry Path Failure like FC Links Down Etc.

Also these paths are used for Dynamic Load Balancing of the IO to the Disk or LUN when DMP Software like EMC Powerpath is used. DMP that is Dynamic Multipathing provides the load balancing apart from providing the Redundancy in case of the path failures.


Regards
Sujit
Viney Kumar
Regular Advisor

Re: show me double entry for each storage point

Hi Sujit

can u provide some example how we can create multipathing for a pv or vg.


Thanks
Viney Kumar
sujit kumar singh
Honored Contributor

Re: show me double entry for each storage point

hi

Multipathing /Alternate links in VG
This feature in LVM prior to 11iv3 provides only Multipathing without Load Balancing.

say there are 2 disks and this is desired to have a VG with those two PVs. But they have 3 Alternate paths each

Disk 1- /dev/dsk/c10t0d1
Alternate paths for the Disk1:
/dev/dsk/c12t0d1
/dev/dsk/c14t0d1
/dev/dsk/c16t0d1

Disk 1- /dev/dsk/c10t0d2
Alternate paths for the Disk1:
/dev/dsk/c12t0d2
/dev/dsk/c14t0d2
/dev/dsk/c16t0d2

Steps of creating the VG shall be like this:

#pvcreate /dev/rdsk/c10t0d1
#pvcreate /dev/rdsk/c10t0d1


Reemeber that pvcreate is reqd on only one path of the Disk or PV if run on the alternate Link for that disk is destructive for the PV and care needs to be taken about identifying the device before pvcreate while working in the MUltipathed devices.

#mkdir /dev/vg02
#mknod /dev/vg02/group c 64 0x0100000
#vgcreate /dev/vg02 /dev/dsk/c10t0d1 /dev/dsk/c10t0d1

Then vgextend the remaining paths of the disk like
#vgextend /dev/vg02 /dev/dsk/c12t0d1 /dev/dsk/c14t0d1 /dev/dsk/c16t0d1 /dev/dsk/c12t0d2 /dev/dsk/c14t0d2 /dev/dsk/c16t0d2

this adds the Alternate paths of the PV in the VG configuration and this can be verified using the command
#vgdisplay -v /dev/vg02

there these Alternate Paths are visible as Alternate Links corresponding to a VG.

HP-UX 11iv1, 11iv2 LVM were capable of provoding a max of 8 Links to a PV in a VG that is 1 Pry Link and the 7 Alternate Links.

LVM in 11iv3 can provide upto 32 LInks to the Same PV.

These Links are called Alternate Links as the IO takes place only via one of the links that is active. In the scenario of a path failure LVM marks that path as failed and IO is Transferred to another Link.

But in 11iv3 LVM provides the Dynamic Multipathing using the Dynamic Persistent Device PSecial files for a PV and upto max of 32 Alternate Links.
Dynamic MEans that A Load balancing for the IO is provided by the LVM and IO is balanced among the IO Paths and all the paths are active.



so we can DMP is inbuilt in 11iv3 which was not there in 11iv2 and 11iv1.

However, Depending on the storage that is being used there are Also Mutipathing Softwares available that if installed and configured can provide the Dynamic Multipathing. For Example

HP XP Disk Arrays : SecurePath XP
HP EVA Disk Arrays : SecurePath EVA
EMC Disk Arrays: EMC PowerPath.


These Softwares provide the DMP.

DMP = Multipathing(Path Redundancy)+ Load Balancing.

For condiguring DMP using these Softwares the commands are respectively:

#autopath -- for SecurepathEVA or SecurepathEVA

#powermt --- for EMC disk arrays.

these commands get installed in the OS once the corresponding Software is installed.

Regards
Sujit




sujit kumar singh
Honored Contributor

Re: show me double entry for each storage point


Hi,


In the Earlier post
----------------------------------------
Disk 1- /dev/dsk/c10t0d1
Alternate paths for the Disk1:
/dev/dsk/c12t0d1
/dev/dsk/c14t0d1
/dev/dsk/c16t0d1

Disk 1- /dev/dsk/c10t0d2
Alternate paths for the Disk1:
/dev/dsk/c12t0d2
/dev/dsk/c14t0d2
/dev/dsk/c16t0d2
--------------------------------------------

actually reads as:

Disk 1- /dev/dsk/c10t0d1
Alternate paths for the Disk1:
/dev/dsk/c12t0d1
/dev/dsk/c14t0d1
/dev/dsk/c16t0d1

Disk 2- /dev/dsk/c10t0d2
Alternate paths for the Disk2:
/dev/dsk/c12t0d2
/dev/dsk/c14t0d2
/dev/dsk/c16t0d2


Regret the inconvenience.

Regards
Sujit