SDDPCM (Subsystem Device Driver Path Control Module) is the multi-pathing plug-in for AIX 5.3 and 6.1.
Customers who use IBM SVC, DS6000, DS8000 and/or ESS800 use this package to allow the operating system to handle multiple paths from OS to storage.
The good news is that this plug-in is supplied free of charge. The bad news is that it is not included with AIX fixpacks.
What this means is that while you may be dilligent with keeping AIX up to date, you may miss SDDPCM in the process.
There are two good reasons to keep SDDPCM in mind when planning updates:
1) Planning an upgrade from AIX 5.3 to 6.1
Before the AIX OS is upgraded, SDDPCM must be uninstalled and then reinstalled after the upgrade. There are cases when the host attachment script must also be uninstalled and reinstalled. This is explained in the SDD Users Guide found here:
If you have already upgraded from AIX 5.3 to 6.1 but you are still using the AIX 5.3 version of SDDPCM, you may need help from IBM before you can upgrade your SDDPCM to the AIX 6.1 version. This will come in the form of some special scripts.
2) General SDDPCM maintenance
As I noted in my previous blog entry, there are quite a few SDDPCM flashes out there right now. You need to check these out and ensure you are not exposed to the issues that are corrected by later versions of SDDPCM. Check out the flashes listed here (or read my previous blog entry):
What about SDD (Subsystem Device Driver) for AIX?
Prior to AIX 5.2 FP5, AIX did not offer native multi-pathing (MPIO). This meant that each hardware vendor had to offer their own third-party software to handle multiple paths. To achieve this with the ESS (Shark), IBM released a product called DPO (Data Path Optimiser). This product became SDD and was made available for a wide variety of operating systems.
When AIX offered MPIO, IBM then also offered a vendor plug-in (Path Contol Module) for native AIX MPIO which IBM called SDDPCM. This means you have two choices with AIX: SDD or SDDPCM. If your considering which is best, SDDPCM is my preference. This is because it is native to the operating system and also better supports the possibility of co-existence of multiple PCMs. Note that migrating from SDD to SDDPCM is not supported by the VIOS at this time, so if your running VIOS you will need to stay put for now.