device file naming on HP/UX and DMX2000 SAN

[Jay_122]

All,
I have a server that I connected to a SAN (EMC DMX2000). When we zoned in the boot disks, the device files started off with C4txdx and c6txdx (primary / alt paths). After we installed the OS and made sure everything was ok, we zoned in the data disks and did an ioscan and an insf -e. After checking this, I noticed that in addition to the c4txdx and c6txdx, there were other device file names c12txdx , c13txdx, c14txdx and c15txdx.

I am new to the SAN environment and have a few questions:

1 - is this expected?
2 - There are only 2 controller cards on this server, what causes the Cx to change?

I have attached the ioscan output from this server. Any help would be appreciated.

Jay

[Torsten. · Accepted solution]

Hi,

looks pretty normal.
Due to the high Volume number in your "SAN" array the system (HP-UX) creates new busses to address them:

Volume Number (LUN): 3/0/4/1/0/4/0.1.8.0.2.2.4 => 276

Here you can see a point where it turns:

disk 58 3/0/4/1/0/4/0.1.8.0.0.15.7 sdisk CLAIMED DEVICE EMC SYMMETRIX
/dev/dsk/c4t15d7 /dev/rdsk/c4t15d7
disk 11 3/0/4/1/0/4/0.1.8.0.1.0.0 sdisk CLAIMED DEVICE EMC SYMMETRIX
/dev/dsk/c12t0d0 /dev/rdsk/c12t0d0

from ... 0.15.7 -> /dev/dsk/c4t15d7
to ... 1.0.0 -> /dev/dsk/c12t0d0


This is the address design.
in cxtydz

d goes from 0..7
t goes from 0..15

if reached, c will be increased.

[Steven E. Protter]

Shalom Jay,

1. Yes
2. I would surmise that the way things are wired there are alternate, in this case two pathes to every disk. This provides confusion and two ways to access the disk in the event of a partial failure of the SAN

SEP

[Jay_122]

Torsten / Steven,
Thank you for all the help. Just two more questions.

1. I am installing power path and would like to use pvlinks as well. Is this ok?

2. With pvlinks, the device used to create the volume group becomes the primary path and all i/o's go down this path. Is this limitation lifted with power path? Meaning, will all the paths to the device be used equally?

Thanks,
jay

[Duncan Edmonstone]

Jay,

1. I am installing power path and would like to use pvlinks as well. Is this ok?

- Yes thats fine - you can use both, although if PowerPath is working correctly you should never see LVM use its PVlinks

2. With pvlinks, the device used to create the volume group becomes the primary path and all i/o's go down this path. Is this limitation lifted with power path? Meaning, will all the paths to the device be used equally?

- Yes, PowerPath will load balance between the different paths automatically.

HTH

Duncan

[Jay_122]

Thanks for all your help