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Using EVA snapshot/snapclone LUN with the same HP-UX v.11.31 agile disk name each time

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Fedon Kadifeli
Super Advisor

Using EVA snapshot/snapclone LUN with the same HP-UX v.11.31 agile disk name each time

From time to time I want to re-create a snapshot of a disk and I want to use this snapshot with the same device name under HP-UX version 11.31 each time. As you know, device files are created with names like /dev/disk/diskXX. Every time I recreate a snapshot and present it to the host (with the the same LUN id), I need to use the 'scsimgr replace_wwid' command.

Is there an easy way to eliminate this problem? For example, can I use the same "World Wide Name" for the new snapshot each time? What is the recommended solution to this problem?
6 REPLIES
Sivakumar MJ._1
Respected Contributor

Re: Using EVA snapshot/snapclone LUN with the same HP-UX v.11.31 agile disk name each time

HP-UX 11.31 uses WWIDs for all devices.

When any SCSI hardware is changed the WWID will change as well. So you can try in using the World Wide Name

This implies to the tape drives as well
For HP Online Case Logging-->http://support.openview.hp.com/
Uwe Zessin
Honored Contributor

Re: Using EVA snapshot/snapclone LUN with the same HP-UX v.11.31 agile disk name each time

The "World Wide LUN Name:" of a virtual disk can be changed, if its unpresented. I can't try it right now, but I am sure you can do the same with an unpresented snapshot.

Let the EVA create one or more value(s) once (be careful - do not try to 'invent' your own values!), save these value(s) in a table for later use and reapply them on new snapshots if needed.

Be careful and make sure that a single server never sees multiple vdisks/snapshots with the same LUN WWN.

Please let us know if it worked.
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Fedon Kadifeli
Super Advisor

Re: Using EVA snapshot/snapclone LUN with the same HP-UX v.11.31 agile disk name each time

Yes, it works. But is this the best solution for having always the agile addressed device name?
Uwe Zessin
Honored Contributor

Re: Using EVA snapshot/snapclone LUN with the same HP-UX v.11.31 agile disk name each time

What do you mean by 'agile addressed device name' ?

A number of operating systems are using the LUN WWN to identify multiple paths and/or differentiate between originals and snapshots/clones.
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Fedon Kadifeli
Super Advisor

Re: Using EVA snapshot/snapclone LUN with the same HP-UX v.11.31 agile disk name each time

Example,

An original disk (LUN) is presented with LUN id 16 on a host. So device names are like this:

# ioscan -m dsf
[...]
/dev/rdisk/disk60 /dev/rdsk/c9t2d0
/dev/rdsk/c11t2d0
/dev/rdsk/c7t2d0
/dev/rdsk/c5t2d0
[...]

A snapclone is created and presented with LUN id 20 on the same host. The device names for the clone become something like this:

# ioscan -m dsf
[...]
/dev/rdisk/disk71 /dev/rdsk/c5t2d4
/dev/rdsk/c11t2d4
/dev/rdsk/c9t2d4
/dev/rdsk/c7t2d4
[...]

Then, the clone is deleted and re-created and presented with LUN id 20 (again) on the same host. The "legacy" device names remain the same (/dev/rdsk/c?t2d4). However the "agile" device name will change to something like /dev/rdisk/disk77. And so on, and so on...

I do NOT want the agile addressed device name (/dev/rdisk/dis71) to change each time I re-create the snapclone.
Uwe Zessin
Honored Contributor
Solution

Re: Using EVA snapshot/snapclone LUN with the same HP-UX v.11.31 agile disk name each time

OK. So HP-UX v11.31 does a 'persistent LUN binding' to the 'agile name' with the help of the 'LUN WWN'.

In that case, yes, I do beleive that reusing the same value for new snapshots is the best way. I would not attempt to fiddle with mapping files withing HP-UX unless this is explicitly documented and supported by HP.
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