Map block devices to iSCSI targets

Tue, Nov 11, 2014

This is just a quick hack but it might be useful to someone. With open-iscsi you can use “iscsiadm -m session -P3” to see which sessions provide which block device, but the output is long and not the easiest to grok.

For example, I have an initiator with 2 LU’s, each LU mapping to a different target. I want to verify which is which because mpathc is giving me less performance than the other.

[root@n10 ]# multipath -ll
mpathb (23533366333336363) dm-6 FUSIONIO, LUN
size=1.4T features='3 queue_if_no_path pg_init_retries 50' hwhandler='1 alua' wp=rw
`-+- policy='queue-length 0' prio=130 status=active
  |- 87:0:0:0  sdb 8:16  active ready running
  |- 88:0:0:0  sdd 8:48  active ready running
  |- 89:0:0:0  sde 8:64  active ready running
  |- 90:0:0:0  sdf 8:80  active ready running
  |- 95:0:0:0  sdg 8:96  active ready running
  |- 96:0:0:0  sdl 8:176 active ready running
  |- 98:0:0:0  sdm 8:192 active ready running
  `- 97:0:0:0  sdn 8:208 active ready running
mpathc (23837616466643737) dm-7 FUSIONIO, LUN
size=1.4T features='3 queue_if_no_path pg_init_retries 50' hwhandler='1 alua' wp=rw
`-+- policy='queue-length 0' prio=130 status=active
  |- 91:0:0:0  sdc 8:32  active ready running
  |- 92:0:0:0  sdh 8:112 active ready running
  |- 93:0:0:0  sdi 8:128 active ready running
  |- 94:0:0:0  sdj 8:144 active ready running
  |- 99:0:0:0  sdk 8:160 active ready running
  |- 101:0:0:0 sdo 8:224 active ready running
  |- 100:0:0:0 sdp 8:240 active ready running
  `- 102:0:0:0 sdq 65:0  active ready running

This represents 2 paths per LU, 4 sessions per path. I cobbled together a quick awk script that maps the targets to the block devices:

# Works with iscsiadm from iscsi-initiator-utils-6.2.0.873-2.el6
iscsiadm -m session -P3 |
  awk -F[:\\t" "] '/Current/ {
    portal=$5
  };
  /Attached/ {
    bdev=$7;
    if (length(bdev) != 0) print portal ": " bdev
  }' |
  sort -t . -k 3,3n -k 4,4n

Which gives me:

192.168.11.5: sdg
192.168.11.5: sdh
192.168.11.5: sdl
192.168.11.5: sdm
192.168.11.5: sdn
192.168.11.6: sdc
192.168.11.6: sdd
192.168.11.6: sdh
192.168.11.6: sdi
192.168.11.6: sdj
192.168.13.5: sdb
192.168.13.5: sdd
192.168.13.5: sde
192.168.13.5: sdf
192.168.13.6: sdk
192.168.13.6: sdl
192.168.13.6: sdo
192.168.13.6: sdp
192.168.13.6: sdq

My targets are differentiated by the final octet, so from this I can gather that mpathb maps to my .5 target, while mpathc maps to my .6 target. I’m coming for you, .6.