$ multipath -ll 3600a0b800011a1ee00003f834a3f7a65
3600a0b800011a1ee00003f834a3f7a65 dm-0 IBM,1815      FAStT
[size=10G][features=1 queue_if_no_path][hwhandler=1 rdac]
\_ round-robin 0 [prio=12][active]
 \_ 2:0:1:4 sdu 65:64 [active][ready]
 \_ 2:0:0:4 sdp 8:240 [active][ready]
\_ round-robin 0 [prio=2][enabled]
 \_ 1:0:1:4 sdk 8:160 [active][ghost]
 \_ 1:0:0:4 sdf 8:80  [active][ghost]
$ # disabled one preferred path
$ multipath -ll 3600a0b800011a1ee00003f834a3f7a65
sdp: rdac prio: inquiry command indicates error
3600a0b800011a1ee00003f834a3f7a65 dm-0 IBM,1815      FAStT
[size=10G][features=1 queue_if_no_path][hwhandler=1 rdac]
\_ round-robin 0 [prio=6][active]
 \_ 2:0:1:4 sdu 65:64 [active][ready]
 \_ 2:0:0:4 sdp 8:240 [failed][faulty]
\_ round-robin 0 [prio=2][enabled]
 \_ 1:0:1:4 sdk 8:160 [active][ghost]
 \_ 1:0:0:4 sdf 8:80  [active][ghost]
$ # ALL GOOD
$ # disabled another preferred path
$ multipath -ll 3600a0b800011a1ee00003f834a3f7a65
sdu: rdac prio: inquiry command indicates error
sdp: rdac prio: inquiry command indicates error
3600a0b800011a1ee00003f834a3f7a65 dm-0 IBM,1815      FAStT
[size=10G][features=1 queue_if_no_path][hwhandler=1 rdac]
\_ round-robin 0 [prio=0][enabled]
 \_ 2:0:1:4 sdu 65:64 [failed][faulty]
 \_ 2:0:0:4 sdp 8:240 [failed][faulty]
\_ round-robin 0 [prio=6][active]
 \_ 1:0:1:4 sdk 8:160 [active][ready]
 \_ 1:0:0:4 sdf 8:80  [active][ready]
$ # failed over to the non-preferred path
$ # that is good
$ # disabled a non-preferred path
$ multipath -ll 3600a0b800011a1ee00003f834a3f7a65
sdu: rdac prio: inquiry command indicates error
sdp: rdac prio: inquiry command indicates error
sdk: rdac prio: inquiry command indicates error
3600a0b800011a1ee00003f834a3f7a65 dm-0 IBM,1815      FAStT
[size=10G][features=1 queue_if_no_path][hwhandler=1 rdac]
\_ round-robin 0 [prio=0][enabled]
 \_ 2:0:1:4 sdu 65:64 [failed][faulty]
 \_ 2:0:0:4 sdp 8:240 [failed][faulty]
\_ round-robin 0 [prio=3][active]
 \_ 1:0:1:4 sdk 8:160 [failed][faulty]
 \_ 1:0:0:4 sdf 8:80  [active][ready]
$ # all good
$ # enabled a non-preferred path
$ multipath -ll 3600a0b800011a1ee00003f834a3f7a65
sdu: rdac prio: inquiry command indicates error
sdp: rdac prio: inquiry command indicates error
3600a0b800011a1ee00003f834a3f7a65 dm-0 IBM,1815      FAStT
[size=10G][features=1 queue_if_no_path][hwhandler=1 rdac]
\_ round-robin 0 [prio=0][enabled]
 \_ 2:0:1:4 sdu 65:64 [failed][faulty]
 \_ 2:0:0:4 sdp 8:240 [failed][faulty]
\_ round-robin 0 [prio=6][active]
 \_ 1:0:1:4 sdk 8:160 [active][ready]
 \_ 1:0:0:4 sdf 8:80  [active][ready]
$ # Good
$ # enabled a preferred path.
$ # expected failback to the preferred path group
$ multipath -ll 3600a0b800011a1ee00003f834a3f7a65
sdp: rdac prio: inquiry command indicates error
3600a0b800011a1ee00003f834a3f7a65 dm-0 IBM,1815      FAStT
[size=10G][features=1 queue_if_no_path][hwhandler=1 rdac]
\_ round-robin 0 [prio=4][enabled]
 \_ 2:0:1:4 sdu 65:64 [active][ghost]
 \_ 2:0:0:4 sdp 8:240 [failed][faulty]
\_ round-robin 0 [prio=6][active]
 \_ 1:0:1:4 sdk 8:160 [active][ready]
 \_ 1:0:0:4 sdf 8:80  [active][ready]
$ # no. failback did not happen. [see the first path group still states "ghost"]
$ # the reason is that the priority of the preferred path group is less than
$ # that of the non-preferred path group.
$ # Basically, non-preferred path is used even though one preferred path is available
$ # which is not correct
$ # wait for a a minute, may be
$ sleep 60
$ multipath -ll 3600a0b800011a1ee00003f834a3f7a65
sdp: rdac prio: inquiry command indicates error
3600a0b800011a1ee00003f834a3f7a65 dm-0 IBM,1815      FAStT
[size=10G][features=1 queue_if_no_path][hwhandler=1 rdac]
\_ round-robin 0 [prio=4][enabled]
 \_ 2:0:1:4 sdu 65:64 [active][ghost]
 \_ 2:0:0:4 sdp 8:240 [failed][faulty]
\_ round-robin 0 [prio=6][active]
 \_ 1:0:1:4 sdk 8:160 [active][ready]
 \_ 1:0:0:4 sdf 8:80  [active][ready]
$ # nope... failback didn't happen.
$ # enabled the other preferred path.
$ # only now the failback happens.
$ 
$ multipath -ll 3600a0b800011a1ee00003f834a3f7a65
3600a0b800011a1ee00003f834a3f7a65 dm-0 IBM,1815      FAStT
[size=10G][features=1 queue_if_no_path][hwhandler=1 rdac]
\_ round-robin 0 [prio=12][active]
 \_ 2:0:1:4 sdu 65:64 [active][ready]
 \_ 2:0:0:4 sdp 8:240 [active][ready]
\_ round-robin 0 [prio=2][enabled]
 \_ 1:0:1:4 sdk 8:160 [active][ghost]
 \_ 1:0:0:4 sdf 8:80  [active][ghost]
$ exit