[CentOS] multipath

Tony Schreiner
Tue, 03 Oct 2017 17:25:43 -0000

I have inherited a system set up with multipath, which is not something I
have seen before so I could use some advice


The system is a Dell R420 with 2 LSI SAS2008 HBAs, 4 internal disks, and a
MD3200 storage array attached via SAS cables. Oh and CentOS 6

lsblk shows the following:
NAME                MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
sdd                   8:48   0 931.5G  0 disk
??sdd1                8:49   0 931.5G  0 part
??mpathi (dm-0)     253:0    0 931.5G  0 mpath
sdc                   8:32   0 931.5G  0 disk
??sdc1                8:33   0  1000M  0 part  /boot
??sdc2                8:34   0  31.3G  0 part  /
??sdc3                8:35   0  31.3G  0 part  [SWAP]
??sdc4                8:36   0     1K  0 part
??sdc5                8:37   0 184.5G  0 part  /home
??sdc6                8:38   0 683.6G  0 part  /data01
sde                   8:64   0 931.5G  0 disk
??sde1                8:65   0 931.5G  0 part
??mpathj (dm-1)     253:1    0 931.5G  0 mpath
  ??mpathjp1 (dm-8) 253:8    0 931.5G  0 part  /data02
sdf                   8:80   0 931.5G  0 disk
??sdf1                8:81   0 931.5G  0 part
??mpathk (dm-2)     253:2    0 931.5G  0 mpath
sda                   8:0    0    51T  0 disk
??sda1                8:1    0  12.8T  0 part
??sda2                8:2    0  12.8T  0 part
??sda3                8:3    0  12.8T  0 part
??sda4                8:4    0  12.8T  0 part
??mpathe (dm-3)     253:3    0    51T  0 mpath
  ??mpathep1 (dm-4) 253:4    0  12.8T  0 part  /SAN101
  ??mpathep2 (dm-5) 253:5    0  12.8T  0 part  /SAN102
  ??mpathep3 (dm-6) 253:6    0  12.8T  0 part  /SAN103
  ??mpathep4 (dm-7) 253:7    0  12.8T  0 part  /SAN104
sdb                   8:16   0    51T  0 disk
??sdb1                8:17   0  12.8T  0 part
??sdb2                8:18   0  12.8T  0 part
??sdb3                8:19   0  12.8T  0 part
??sdb4                8:20   0  12.8T  0 part
??mpathe (dm-3)     253:3    0    51T  0 mpath
  ??mpathep1 (dm-4) 253:4    0  12.8T  0 part  /SAN101
  ??mpathep2 (dm-5) 253:5    0  12.8T  0 part  /SAN102
  ??mpathep3 (dm-6) 253:6    0  12.8T  0 part  /SAN103
  ??mpathep4 (dm-7) 253:7    0  12.8T  0 part  /SAN104

sda and sdb are two views of the unit on the MD, sdc is the boot and root
disk, one of the disks sde (mpathj) has a mounted file system, the
remaining two do not.
here is df:
Filesystem           Type   Size  Used Avail Use% Mounted on
/dev/sdc2            ext4    31G   26G  4.0G  87% /
tmpfs                tmpfs   16G   92K   16G   1% /dev/shm
/dev/sdc1            ext4   969M  127M  793M  14% /boot
/dev/sdc6            ext4   673G  242G  398G  38% /data01
/dev/mapper/mpathjp1 ext4   917G  196G  676G  23% /data02
/dev/sdc5            ext4   182G  169G  3.9G  98% /home
/dev/mapper/mpathep1 ext4    13T   11T 1005G  92% /SAN101
/dev/mapper/mpathep2 ext4    13T  5.0T  7.0T  42% /SAN102
/dev/mapper/mpathep3 ext4    13T  4.9T  7.1T  42% /SAN103
/dev/mapper/mpathep4 ext4    13T  8.2T  3.8T  69% /SAN104


So a few questions:

Is there any value in using multipath on the 4 internal drives; do they
actually have multiple data paths?

Why does multipath not create a mpath device for the system disk sdc, there
is no blacklist in the mulitpath.conf file.
If I do a dry-run mulitpath -d command, it sets up mpathh on sdc, but
apparently not on boot. Why not?
I should say that the system has not been rebooted since well before I took
it over, it has been up for over 400 days.

the sdd and sdf disks have a single partition, but apparently no mpath
device for the partition, how to I create one?


Thanks in advance