mpath on RHEL

[DanGiles]

Can anyone recommend some GOOD documentation (or a tutorial!) on configuring multi-pathing on RHEL? The docs I could find aren't very good at explaining things. For instance, you have a choice for active/active using round-robin or queue depth (to name just a couple), but why one over the other?

Right now I have 22 volumes being presented to the server across 8 paths, so I get 176 sd devices. When you put multi-path on top, one would expect to get 22 dm devices, but there are 44. I need to know what's going on and how to fix it.

 

[Stephan]

Hi Dan. Which RHEL are you running? Also, where or rather what is providing your LUNs? Some options depends on the type of array behind the LUNs, like an active active array, or active passive etc...i've included a pdf i found a while ago...may be of some help.

 

[DanGiles]

I found what I needed in the lvm manual. This along with 'df -h' gives me the filesystem->mpath mapping I'm looking for.

dmsetup info -c -o name,blkdevs_used

No where in anything I read did it imply that you could have multiple dms for the same mpath