topic Re: Snapclone On EVA in HPE EVA Storage

Snapclone On EVA

Mme Jonnaert — Wed, 18 Feb 2004 12:31:33 GMT

We want to use the snapclone feature on a Eva under hp/ux itanium servers.
We have heard about problems with the controllers and their intensive usage when using this option.
have you informations about that?
thanks
tmj

Re: Snapclone On EVA

Uwe Zessin — Wed, 18 Feb 2004 13:19:10 GMT

Doing the clone puts an additional burden on the controllers and disks. Also, if I recall correctly, you cannot present the clone to the same server under UP-UX. Well, many operating systems cannot cope with 'redundant' meta data on the disks.

In our lab I once had a Windows server stalling the access to a LUN from which a snapshot was taken, but that was due to an old version of Secure Path.

There might be a problem when you are creating multiple snapshots of the same LUN. There is a special way to toggle the snapshot cache to write-through, but it will decrease performance to the parent LUNs. I would not make such a change without a real need. See if you can test your whole configuration under load before you put it into real use.

I'll be doing a BC EVA implementation with HP-UX PA-RISC servers in about 2-4 weeks. While we very likely will not use clones you might be interested in the results anyway?

Re: Snapclone On EVA

Orrin — Wed, 18 Feb 2004 21:48:53 GMT

Hi Tmj,

The snapclones are faster for smaller LUN Sizes... on the same DG.

A good alternative si to use the clone feature in Vxfs, you can achieve all the same functions without the additional space overhead of the snapclone.

Hope this helps..

Regards,
Orrin.

Re: Snapclone On EVA

Mike Naime — Wed, 18 Feb 2004 23:38:34 GMT

Snapshot = Space conservative and almost no time to make. We use this!

Snapclone = Full copy that takes time to make. If you are attempting to make a backup copy of a 500GB database, this can take a couple of hours to create.

While the snapclone is available almost immediately for usage, your EVA performance will be degredated until the copy is completed. We DO NOT use this!

Re: Snapclone On EVA

JJ Urich — Fri, 26 Mar 2004 14:51:04 GMT

I'd like to humbly correct Uwe's statement about not being able to mount snapclone's on the same host... This most certainly can be done in HPUX. I haven't done it with an EVA, but do it routinely with EMC's, XP's, and VA storage systems. HP wrote a command called vgchgid for when EMC for came out with the BCV (business continuity volume) for hpux 5-10 years ago. This command changes the VGID that is saved in the VGRA (volume group reserved area) or at least that where I think it is stored...

To use it just do "vgchgid /dev/rdsk/c0t0d0" then do your vgimport, vgchange, fsck, mount.

Cheers,

JJ

Re: Snapclone On EVA

Uwe Zessin — Fri, 26 Mar 2004 15:32:55 GMT

Ah. That's good to know. The BC administration guide explicitly states that it is not supported by BC itself. I will keep this in mind when I get back to the system administrator with whom I should implement BC.

I am not familiar with LVM - what is one supposed to do when the VG is made of multiple PVs?