topic Re: XP24000 Thin Provisioning & External Storage in Disk Enclosures

XP24000 Thin Provisioning & External Storage

Dean.V.Kelly — Fri, 04 Sep 2009 14:05:18 GMT

I'm new to the practice of ThP on the XP series and have been delivered a solution to implement, but can't quite see how it's possible.

The basic upshot is that I have an XP24K with an EVA4400 attached as external storage. I've been tasked with building ThP pools/V-VOLs on the internal and external devices and setting up BC to replicate from the XP to the EVA.

I've managed to build my V-VOLs on the internal XP disks with no problem, but try as I might I don't seem to be able to build V-VOLs on the EVA.

When I build a pool and select the CU which our EVA Storage is assigned to I don't see any LDEVs I can assign to the pool.

Am I missing something or is it not possible to create ThP pools on External devices?

Thanks in advance,
Dean

Re: XP24000 Thin Provisioning & External Storage

Dean.V.Kelly — Fri, 04 Sep 2009 14:13:33 GMT

As a second question: Is there a "best practice" whitepaper that covers ThP on the XP24K that anyone knows about?

Re: XP24000 Thin Provisioning & External Storage

Nigel Poulton — Fri, 04 Sep 2009 16:45:28 GMT

Hi Dean,

The more information the better......

First question that springs to mind is how big are the LDEVs that are mapped from the EVA?

As for a best practice guide...... Ive attached a paper that I wrote a little while ago on the subject.

HTH

Nigel

Re: XP24000 Thin Provisioning & External Storage

Dean.V.Kelly — Tue, 08 Sep 2009 08:44:18 GMT

Nigel,

thanks for your best practice document - it solved my problem (the LDEVs I was using to create the pool were too small, which your document clearly indicated).

Could I trouble you to clarify a couple of details, please? From reading your notes it's inferred that a ThP pool should always consist of the entire contents of a PG (although the array will allow to just use a few LDEVs from a PG if you want to) - did I read that correctly?

Secondly, there're mention in your notes that only at a certain release is the expansion of LDEVs in a ThP pool supported and at certain releases only the last LDEV can be expanded. Can you confirm which ucode releases expansion is supported at and to what degree, and is that expansion done as a LUSE? We have ucode main:60_04_13 svp:60_04_12/00 Server:05_04_00

Thanks again for your help
Cheers,
Dean

Re: XP24000 Thin Provisioning & External Storage

Nigel Poulton — Wed, 09 Sep 2009 15:51:33 GMT

Hi Dean,

Glad that you read the doc and managed to use it to fix your issue.

Its a performance best practice to allocate all of the space in an Array Group to either ThP use or classical LDEVs. Yes the GUI wi let you mix and match but its not recommended. Back in the early days of ThP the BP was to create ThP Pools with 16 Array Groups and each Array Group to have 16 equally sized LDEVs (thus making 256 ThP Pool-VOLs, 256 was the initial limit). This is not longer deemed necessary and the most recent recommendation I would give would be to create a single large LDEV taking up all the space in your AG and allocate that LDEv to ThP. Does that answer your first question?

ThP running on recent versions of ucode (v4 and later I think) allow you to expand the last LDEV in a V-VOL Group. This expansion is not via LUSE. You can simply increase the size of the V-VOL. Although this is only supported on certain OS's.

Check out the following link that explains V-VOL Groups and why only the lastV-VOL in a V-VOL Group can be expanded - http://blogs.rupturedmonkey.com/?p=190

v5 has some new features including auto-relevelling when adding more capacity to pools etc..... Making some of the things I say in the doc obsolete when using v5 of code. I'll be updating the doc in the future.

Hopefully that helps.

PS. Its good courtessy to assign points to answers. Normally I wont answer if I see people arent allocating to previous answers, but as you used the doc and worked out your prob for yourself Ive replied again.

Re: XP24000 Thin Provisioning & External Storage

Dean.V.Kelly — Mon, 14 Sep 2009 07:55:00 GMT

Nigel - thanks again.

Sorry about the lack of points: my question was the first one I've raised on the Forum and I wasn't aware of the points system.

I've allocated points to both replies you gave.

Once again - thanks for your help; it's been invaluable.