AIX 5.3 MPIO vs RDAC on DS4000 range


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# 1  
Old 10-08-2008
AIX 5.3 MPIO vs RDAC on DS4000 range

Hi

I would like to ask what the benefits are of changing from RDAC to MPIO when connecting to a DS4000 on AIX 5.3? I have heard that IBM MPIO "might" support more than 1 active path to a LUN when connecting to a DS4800 through more than 1 host connection on the same AIX client. I understand that this will require specific AIX levels as well as DS4000 firmware levels. I am currently converting from 2 seperate VIO servers in one system to dual redundant path VIOS. Thus I will need MPIO on the VIO clients. However is it advised to run MPIO on the VIOS as well? and are there benifits in changing to MPIO on AIX 5.3 from RDAC?

Thanx
# 2  
Old 10-08-2008
Since MPIO has load balancing and path failover functionality, it will accept more than 1 path for sure. And yes, you can install it on VIO afaik.
We are not sharing any disks via VIO - only hosting some adapters for our admin LAN with SEA FAILOVER.
Usually we provide for our boxes direct access via MPIO or PowerPath to our SAN storage.

I don't know anything about RDAC, but when you just Google for AIX VIO and MPIO, you find a lot of documentation and also this thread, that might be helpful:
MPIO or RDAC for DS4800 - ITtoolbox Groups

Also 2 Redbooks that might help:
IBM Redbooks | PowerVM Virtualization on IBM System p: Introduction and Configuration Fourth Edition
IBM Redbooks | IBM System Storage N series MPIO Support?Frequently Asked Questions
# 3  
Old 10-08-2008
Hi Zaxxon

Thanx for the feedback.

I understand that MPIO will provide more than 1 path but I am trying to figure out if the other paths will all be only fail-over or if I can have 4 paths to each LUN(2 from each controller A and B) through 2 different host connections on the DS4800? That config is now supported with the new DS4000 firmware and AIX 5.3 TL08 (I think) and above. However I can not find confirmation if the 2 paths that connect to the same controller (lets say controller A) will both be active (LUN assigned to controller A in Storage Manager) with the other 2 paths(to controller B) acting as fail over paths? or if you can still only have 1 active path on a DS4000? Hope I'm making sense here ?
I also get some references to using SDDPCM on AIX? But I can not find an official IBM link stating that it's support on AIX. It is however supported on windows.

thanx
# 4  
Old 10-08-2008
MPIO is part of the AIX 5.3 OS. It provides access to volumes through multiple physical paths while those devices appear as single hdisks. Supported policies are failover or round-robin but no load balancing. The latter is added by SDDPCM. However, with DS4K you are bound to use RDAC. SDDPCM can be used with DS6K and DS8K only.
# 5  
Old 10-08-2008
hello,

we are running sddpcm on ds4700/ds4300 behind the svc. it works quite well and we've noticed considerable performance gains in I/O. we also have some environments running on js22's with one vios serving sddpcm I/O out to 2 lpars.

before the svc, we were using rdac with active/passive on the ds4000.
# 6  
Old 10-08-2008
Quote:
Originally Posted by dig1tal
[...] we are running sddpcm on ds4700/ds4300 behind the svc. it works quite well and we've noticed considerable performance gains in I/O. [...] before the svc, we were using rdac with active/passive on the ds4000.
Interesting setup but still no load-balancing. Do you use other san storage beside the DS4K or what else is the reason for using SVC?
# 7  
Old 10-09-2008
Quote:
with one vios serving sddpcm I/O out to 2 lpars
Hi Dig1tal

I see you said that you have a VIOS running SDDPCM, is that correct? and if so what storage is that connected to? or does the VIOS also get its disks from the SVC?

The reason I ask is that there seems to be some confusion as to SDD/SDDPCM and AIX support for the DS4000 range. This is mainly due to the fact the windows does support SDDPCM for the DS4000 but I don't think AIX does in a direct attached mode (no SVC), as Shockneck also stated.

thanx
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