Multi pathing to SAN.

[Christof Schoeman]

Hi

We are planning to migrate from Tru64 to HP-UX. We want to do some testing with regards to multi pathing, but I am hoping to hear what other people out there are doing.

Some questions:
- Can VxVM do this by itself?
- How about file systems (JFS, VxFS...)
- Do we need Powerpath (EMC)?
- Does anyone use Secure Path?
- Are there any future plans to introduce a single device mechanism as in Tru64?

Hope you can help.

[Luk Vandenbussche]

Hi Christof,

It is important to know what type of SAN you are using? Depending on this the multipath options are different. Can you provide this info

[Christof Schoeman]

EMC Symmetrix/DMX and EMC Clariion.

[Arunvijai_4]

Hello,

You can use Powerpath to configure Multipathing. I dont think, VxVM will do this by itself.

-Arun

[Shameer.V.A]

Hi Christof,

VxVM is having the feature of DMP ( Dynamic Multipathing)

Regards,

Shameer

[Luk Vandenbussche]

Hi Christof

- VxVM support multipath
- Filesystems have no problems with multipath
- Powerpath is the tool for EMC, check with them what the interaction is with Vxvm if you plan to use this
- Securepath is for HP Storage

[Christof Schoeman]

Thanks, I'm having a look at what DMP entails.

Luq, you say that filesystems do not have problems with multipathing. Which filesystem? Does it automatically detect multiple paths to the same device?

[Devender Khatana]

Hi,

Can Vxvm handle this by itself?

VxVm can not do anything about it unless your hardware is configured to support it. You should use multipath/secure path depending upon the vendor and then should make multiple devices available to the hosts.

VxVm DMP will help only in accessing a disk by one device file, allthough it would have 4-8 other device files on the same host. It will also provide load balancing among paths and the failover to other paths.

To see the available paths on the host use
#vxdmpadm listctlr all

Also DMP is not there in standard bundle of VxVm. You should have full licensed version to use DMP.

HTH,
Devender

[Luk Vandenbussche]

Christof,

Mulitpath is handled at volumegroup level.
In a volumegroup you can create HFS and JFS logical volumes without any multipath option specified here

[Alzhy]

Peace Christof.

First let me say that Filesystems (VxFS, JFS, HFS, raw) are not dependent on the underlying volume manager (LVM or VxVM). Multipathing (or path protecttion, load balancing) is either the a function of the volume manager OR the "drivers" of the storage (i.e. PowerPath, SecurePath, etc.).

Since you seem to be interested with the DMP features of VxVM - please note that you will only have DMP functionality and all the niceties of VxVM "understanding" your array IF you're running the full VxVM release AND has the correct ASL (or array support library).

When I used to work with EMCs, it was my understanding that you can do away with PowerPath if you set the mode of the EMC LUNs to DMP compatible mode. This "DMP mode" presents the LUN with different serial numbers -- which is the basic ingredient for DMP to interact with the multiple paths of a LUN for purposes of load balancing, path selection and failover.

Check with EMC/Veritas if this is still true. Depending on the EMC model you have or plan to purchase - it may be possible to do away with PowerPath and just use VxVM's DMP.

[Christof Schoeman]

Hi all

Thanks for your input.

It seems that the choice of multipathing mechanism depends on whether I will be using file systems or raw devices (see discussion of this at http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=992511).

For file systems (UFS or JFS/VxFS), I would use Powerpath, and for raw, I can use VxVM/ DMP. Or, of course, I can put file systems on top of VxVM/DMP.

Let me know if you know of other/better ways of doing this.