topic Re: powerpath problems in Operating System - HP-UX

powerpath problems

anat heilper — Mon, 17 Dec 2007 14:25:59 GMT

Hi,
I've installed powerpath on hpux 11.23 pa-risc ( without MCSG)
can someone explain what actually happens after I issue the command powermt config?
i understand that the data base of teh powerpath is built, but suppoe I want to attach to a disk, what path should I give it so it won't be aware of the multipathing?
(because no new device is reated, as appose to Linux, Aix and solaris os)

Thanks,
Anat

Re: powerpath problems

Geoff Wild — Mon, 17 Dec 2007 14:39:20 GMT

PP is fairly simple...it works at a lower level then the device path - so it doesn't really matter which one you use. I tend to just grab the first one in the output of an inq command.

Rgds...Geoff

Re: powerpath problems

Shahul — Mon, 17 Dec 2007 14:43:13 GMT

Hi,

If you have EMC powerpath installed and multiple physical paths to the array, then you will see multiple paths in ioscan command, try these,

#ioscan; insf -e

For example, if you have 50 disks with two paths each, you should see 100 devices, as powerpath sits below LVM, you don't need to worry what device is used in LVM. Powerpath will manage that, even if the path in LVM is dead, still it's OK.

powermt display will give you the details about paths.

Good luck
Shahul

Re: powerpath problems

anat heilper — Mon, 17 Dec 2007 15:32:45 GMT

Hi,
Thanks for your answers.
I want to use powerpath without LVM, with oracle asm.
If a device is not generated for the virtualization of the paths, how does the asm application attaches to a device ( it doesn't support multipath according to its documentation)?

Thanks,
Anat

Re: powerpath problems

Hasan Atasoy — Mon, 17 Dec 2007 15:43:27 GMT

hi anat ;
on oracle asm side use first paths of the disks . for example you have 2 path for a disk namely /dev/dsk/c4t?d? and c4t?d? . pp will control to access to disk devices. if c4 paths fails , although you define c4 path in asm your io will go from c6 path but you will not get any error for c4.

Hasan.

Re: powerpath problems

Geoff Wild — Mon, 17 Dec 2007 15:51:43 GMT

Make sure that ASM is supported on PowerPath - check with EMC and Oracle.

Technically - it should "work" - as PowerPath automatically switches and balances the I/O across all the paths to a device.

Like LVM, for ASM you would only need to supply 1 of the devices to a disk.

Rgds...Geoff

Re: powerpath problems

anat heilper — Mon, 17 Dec 2007 16:05:40 GMT

Hi,
ASM is supported on PowerPath. however, asm doesn't support multipath, it relies on a multipathing driver, such as powerpath, which is recommended in the release notes of powerpath. so I want to understand how does this application attaches to the device?

Anat

Re: powerpath problems

Duncan Edmonstone — Mon, 17 Dec 2007 21:28:56 GMT

Anat,

You already have your answer... just pick one of the devices - so if you have a disk which appears as /dev/rdsk/c4t6d0 and /dev/rdsk/c8t6d0 then just pick one of those for ASM - PP will take care of failing over to the other path for you.

Some people like to make this neat by doing something like this:

mkdir /asm
ln -s /dev/rdsk/c4t6d0 /asm/disk1

Then set the ASM parameter ASM_DISKSTRING to /asm/disk*

HTH

Duncan