I asked the exact same question on this forum about 6 months ago, but haven't got a single reply. 😞
Microsoft is a bit vague about it, but in their document "Windows Server High Availability with Microsoft MPIO" on www.microsoft.com/mpio they say:
"Multipath software suites available from storage IHV’s typically provide an additional value add beyond the implementation of the MSDSM as the software typically also provides auto configuration, heuristics for specific storage arrays, as well as statistical analysis, and integrated management, It’s generally recommended to use the DSM provided by the hardware storage array partner to achieve optimal performance since the storage array partner can make more advanced path decisions in their DSM specific to their array."
NetApp says something similar in their documentation on MPIO.
Microsoft DSM has a few benifits as well:
- cheaper (builtin feature of WIndows 2008)
- ALUA aware (ONTAP DSM isn't, strangely)
We decided against using Microsoft DSM. Breaking point being the recommendation of both companies to use the vendor's DSM.
Data ONTAP does not currently support ALUA for iSCSI paths. Because the ALUA setting must be the same for all paths to a LUN, mixed FC and iSCSI paths to the same virtual disk (LUN) are not DSM supported with DSM 3.4. You can still have FC paths to some LUNs and iSCSI paths to other LUNs from the same Windows host.
IHV's DSM's have an advantage in terms of their understanding of the Storage Array Hardware/Firmware.An example being in moving LUNs between controllers during failover or failback using Mode Pages,handling Auto Volume Transfer etc.There are also plenty of timeout related settings for the Storage Box that IHV' DSM's know better.Also there could be some specific load balancing technique that IHV's know better because of their understanding of the Storage behavior to increase I/O throughput.
Server 2008 has built-in MPIO and there is MSDSM that can be made to load for IHV's hadware ID's.However for the above reasons IHV's DSM could be preffered.