StorWize v3700 and Power8 (S822) AIX, configuration best practice for LUNs?
Hello,
We have an Power8 System (S822) and a IBM StorWize v3700 SAN.
The OS is AIX 7.1.
With this hardware from what I read I need to download/install special SDDPCM drivers, so I did (SDDPCM VERSION 2.6.6.0 (devices.sddpcm.71.rte).
I carved my volumes in the StorWize and presented to my single host (the SAN is directly connected via FC to the host). There is no virtualization of any kind, single bare bone AIX OS install.
The whole process was fairly easy, carve the RAID 10 LUNs, map to host, then in the host after I installed the SDDPCM drivers I run "cfgmgr" and LUNs get detected, from there I create the VGs and JFS2 filesystem.
Now if I look at the attributes of my "hdisk4" LUN..
Some PCMPATH data..
My question is about the "algorithm", currently (by default) this is set to load_balance.
The host (S822) has a dual FC path to each canister on the V3700. The additional enclosures on the V3700 also have dual path via SAS to each other enclosure's canister. So the idea is we can loose one path and continue to operate without downtime.
Now if algorithm = load_balance and a single path fails (lets say I unplug 1 of the FC cables), what will happen? Will it switch into failover or must I set this to "failover" at the start?
If the algorithm is "failover", is only 1 path active and the other on stand-by?
My goal is to have full redundancy.
Any experts able to give some feedback?
---------- Post updated at 06:31 PM ---------- Previous update was at 06:20 PM ----------
Oh almost forgot to mention vg_root is not off the SAN, the host has 2 internal disks that I've setup for vg_root.
Moderator's Comments:
edit by bakunin: this is hardly "Unix for Dummies" and it is very AIX-specific. I transfer this thread over to the specialized AIX board.
---------- Post updated 03-04-15 at 12:50 PM ---------- Previous update was 03-03-15 at 06:31 PM ----------
It seems that according to this article Guide to selecting a multipathing path control module for AIX or VIOS I could leave this as "load_balance" and loose a path, the PCM can auto detect dead paths and recover them when they are back up without user interaction. Time to test
Just to clarify, since this is not OS related, load_bal it is an algorithm which is used to send I/O requests to disks using FC paths.
In this case it will keep track which path has less load to issue I/O over it.
If it has only one path active due some fault, it will not use any algorithm to balance the traffic, since it is not needed. There is only one path to issue I/O commands over.
Given the mess SDDpcm + HAS can make with being forgotten during AIX updates, or especially during AIX migrations, and that the SDDpcm code is already being integrated into AIX native MPIO, I'd have to think long and hard about whether it's even worth installing these days.
Either way AIX / SDDpcm will cope with lost paths in much the same way as each other, as long as there is an available path you should have nothing to worry about.
Oh, and things like dynamic tracking and fast fail for the fibre interface attributes and the way the two interact.... IBM Knowledge Center
Lots to read, several decisions to make, please feel free to keep discussing things here if anything is unclear - I appreciate it's a bit of a mine field when you are new to this arena.
Thanks for this, I was under some time pressure and I ended up going with the SDDpcm drivers for the SAN hdisks as suggested by IBM TS and things are looking good so far.. I left the other parameters such as the load balancing policy all to the defaults.
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