How many paths per LUN?

[essilor]

Hello! experts,
I have a question. Does anyone know how many paths per LUNs does HP recommend as best pratices?

Also, does anyone know the timeout value for PV to be set as part of best practices? The document suggests 30 secs., but someone told me 60 secs.?

Any thoughts?

Thank you.

[Torsten.]

You want to know recommendations, but you don't tell us important information like OS, version, storage device ...

Some more details, please!

[essilor]

Dumb me!

OS: HP-UX 11i
Storage: XP12000

[Thomas J. Harrold]

You are allowed a maximum of 8 pvlinks to a LUN. Beware that depending on your storage array, you can have multiple controllers presenting the same LUN. You can have multiple HBAs to "see" the LUN.

Depending on how you configure your SAN, it's not impossible to hit 8 PVlinks quickly!

At a minimum, I'd recommend 4 total paths (one primary + 3 alternates) to each LUN.

You should be able to sustain a failure in an HBA, or in a storage controller, or anywhere inbetween, and still have access to the LUN.

Don't change the PV timeout, unless you have a good reason, such as a recommendation from your storage vendor. (EMC likes larger values, for example)

-tjh

[essilor]

Okay. Now though adding more paths to each LUN from different ports and provide redundancy, does it in any shape or form provide any performance enhancement?

On XP12000, we have not stripped the data across RGs. Also, we believe we are not out running the fiber bandwidth.

That brings up another question. Does anyone know if any product to measure the throughput of the fiber controller on HP-UX 11i?

[krusty]

HI Essilor,

I think Thomas did a great job of answering you, however I would disagree on changing the timeout value. I've installed XP's since they came out and we have always changed the timeout value to 60 sec (the default is 30 sec). Sometimes customers will even increase this as high as 180 based on there application, but 60 is a good start. I would highly recommmend you change the this value using the pvchange -t command.

HTH,

Curt

[Zinky · Accepted solution]

Essilor,

Peace and Clean Earth!

How many Paths per LUN (in your case XP12000 LUNS) is considered optimal?

It depends:

1) What Volume Manager and Path Protection your're using.

If you're using VxVM with DMP (dynamic multi pathing), then it's the XP's preferred pathing/"load-balancing" environment. VxVM will try to optimize usage of every LUN's available paths to your array.

2) How your Applications drain storage juice out of your XP12K.

For DB (i.e. Oracle), I will separate redo logs, archive logs and identified hot/superhot storage units (filesystems and raw volumes) to their own path/channel.


Generally however, I've yet to see a 2Gbps FC channel get overloaded. This you can do BTW using the Fabric Switch's tools where you can brow per port statistics of ports going to your HBAs and ports going to the XP.

On our largest servers (~ 10TB single server environments), 4 x 2 FC HBAs have so far been more than sufficient.

BTW, we always stripe our main db storage units accross LUNS presented on different "array groups" and ACP's.

Hope this helps and kudos to your having an XP12000!

[essilor]

Thank you guys.

[Zinky]

Essilor, BTW with VxVM and XP12K and HP-UX - I believe you can have up to 32-paths for every LUN presented.. I however do not know if it is really practical nor have I actually tried it.