Interpreting DM-Multipath output in Linux

Posted by satish on Jan 24, 2019; 5:12am
URL: http://erman-arslan-s-oracle-forum.124.s1.nabble.com/Interpreting-DM-Multipath-output-in-Linux-tp7143.html

Dear Erman,

Recently,i was introduced to multipathing in our production environment and had not heard about this earlier.After some digging,i think i am starting to get a handle on how the concept works in theory but having trouble if i look into the box and need your support

from multipath -11,Got below output

PRD-DATA19 (360002ac0000000000000007e0001c9fc) dm-46 3PARdata,VV
size=100G features='1 queue_if_no_path' hwhandler='1 alua' wp=rw
  |- 2:0:0:53 sdar 66:176  active ready running
  |- 1:0:1:53 sdff 130:16  active ready running
  |- 2:0:1:53 sdcy 70:96   active ready running
  `- 1:0:0:53 sdhm 133:192 active ready running


From theory,When you have multiple paths to a LUN, Linux creates a SCSI device for each path. This means that a single LUN might appear as/dev/sdar,/dev/sdff,/dev/sdcy,/dev/sdhm if there are four paths to it. To make it easy to keep track of the LUNs, DM-Multipath creates a single device in /dev/mapper/ for each LUN that includes all the paths.
For example, /dev/mapper/360002ac0000000000000007e0001c9fc is the multipath device that is created on top of /dev/sdar,/dev/sdff,/dev/sdcy,/dev/sdhm

1)Are the below scsi devices physical? OR just the names assigned by Linux?
sdar,sdff,sdcy,sdhm

2)Upto my knowledge,all these four cane be called as paths to a storage lun(360002ac0000000000000007e0001c9fc)?

3)Can we identify what the scsi device that is mapped to this lun(360002ac0000000000000007e0001c9fc)

4)In above,case i have 100GB lun assigned?please correct me if am wrong

Thank you