RHEL4 multipath -ll "active" vs "enabled"?

[Trever Furnish]

Can anyone tell me the significance of "active" versus "enabled" in the output of multipath -ll on RHEL4U6?

We've noticed that sometimes the word on one of the 'round-robin' lines in the output of multipath -ll will change from "active" to "enabled" and visa versa. For example:

mpath5 (3600508b40008ac830000700000820000)
[size=2 GB][features="1 queue_if_no_path"][hwhandler="0"]
\_ round-robin 0 [prio=100][enabled]
\_ 3:0:1:4 sdaw 67:0 [active][ready]
\_ 1:0:1:4 sds 65:32 [active][ready]
\_ round-robin 0 [prio=20][enabled]
\_ 3:0:0:4 sdah 66:16 [active][ready]
\_ 1:0:0:4 sdd 8:48 [active][ready]

...will change to:

mpath5 (3600508b40008ac830000700000820000)
[size=2 GB][features="1 queue_if_no_path"][hwhandler="0"]
\_ round-robin 0 [prio=100][active]
\_ 3:0:1:4 sdaw 67:0 [active][ready]
\_ 1:0:1:4 sds 65:32 [active][ready]
\_ round-robin 0 [prio=20][enabled]
\_ 3:0:0:4 sdah 66:16 [active][ready]
\_ 1:0:0:4 sdd 8:48 [active][ready]

I know it's difficult to spot, but what's changed between those two is that on the first "round-robin" line in each listing, the word "enabled" changed to "active".

Can someone shed light on the significance of that change?

[Matti_Kurkela]

The "round-robin" line identifies a path group.

On a RHEL4 machine with the multipath tools installed /usr/share/doc/device-mapper-multipath-/Multipath-usage.txt has this information about multipath group states:

---

Path Group States:

active - Path group currently receiving I/O requests.

enabled - Path groups to try if the active path group has no paths in the ready state.

disabled - Path groups to try if the active path group and all enabled path groups have no paths in the active state.

NOTE: The disabled state only exists for certain storage arrays.

---

So, both "active" and "enabled" seem to be good states to be in, but "active" has the additional meaning that something is using that path group right now. (But what happens if there are no I/O requests to the multipathed disk?... hmm...)

Is your system quiet (no processes accessing the multipathed disks) when you typically see "enabled" instead of "active" on the top path group?

Are there any multipath-related messages in the syslog or in the "dmesg" command output?

MK

[Trever Furnish]

Thanks! Those are great clues.

We're actually only monitoring this by collecting the output of multipath -ll and diff'ing it once per hour, so it could change many times in the interim (between collections) and we'd never notice.

It doesn't seem to correlate to any messages in syslog or dmesg, but I'm going to start watching more closely there -- maybe I'll see something I've missed.