multipath and sysfs device dependency

hahacc · 11-03-2015, 04:30 AM

Hi Folks,
One of our server is using multipath, take dm-5 for example, we can see only one path found:

Code:

[root@test ~]# multipath -l
3600605b00a2f47e0000c5e9a0ba779b5 dm-5 LSI,MR9361-8i
size=1.1T features='0' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=1 status=active
  `- 0:2:7:0 sdh 8:112 active ready running

And from sysfs, dm-5 holds dm-14 & dm-15:

Code:

[root@test ~]# ls /sys/block/dm-5/holders/
dm-14/ dm-15/

And below is from dmsetup ls:

Code:

[root@test ~]# dmsetup ls
3600605b00a2f47e0000c5e9a0ba779b5       (252, 5)
3600605b00a2f47e0000c5e9a0ba779b5p1     (252, 14)
3600605b00a2f47e0000c5e9a0ba779b5p9     (252, 15)

I'm a little confused about sysfs output, could anyone help me out of this?

Thanks!

berndbausch · 11-03-2015, 08:53 AM

The sysfs output means that dm-5 is held by dm-14 and dm-15, not that it holds them. dmsetup ls reveals that they are partitions created on top of dm-5.

On the other hand, you would see that dm-5 holds sdh.

hahacc · 11-03-2015, 08:48 PM

Quote:

Originally Posted by berndbausch

The sysfs output means that dm-5 is held by dm-14 and dm-15, not that it holds them. dmsetup ls reveals that they are partitions created on top of dm-5.

On the other hand, you would see that dm-5 holds sdh.

Thanks, proved from another DM multipath device dm-0:

Code:

[root@test ~]# multipath -l
3600605b00a2f47e0000c5e820a4351fe dm-0 LSI,MR9361-8i
size=1.1T features='0' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=0 status=active
  `- 0:2:2:0 sdc 8:32  active undef running

[root@test ~]# blkid|grep 3600605b00a2f47e0000c5e820a4351fe1
/dev/mapper/3600605b00a2f47e0000c5e820a4351fep1: UUID="da2359ef-815f-455d-9402-d28031129afd" TYPE="ext3" SEC_TYPE="ext2"

[root@test ~]# ls /sys/block/dm-0/holders/
dm-17  dm-18

[root@test ~]# cat /etc/fstab|grep da2359ef-815f-455d-9402-d28031129afd
UUID=da2359ef-815f-455d-9402-d28031129afd /extend2 ext3 defaults 0 0

[root@test ~]# dmsetup ls
3600605b00a2f47e0000c5e820a4351fe       (252, 0)
3600605b00a2f47e0000c5e820a4351fep1     (252, 17)
3600605b00a2f47e0000c5e820a4351fep9     (252, 18)

[root@test ~]# fdisk -l /dev/sdc

    WARNING: GPT (GUID Partition Table) detected on '/dev/sdc'! The util fdisk doesn't support GPT. Use GNU Parted.


    Disk /dev/sdc: 1198.9 GB, 1198999470080 bytes
    255 heads, 63 sectors/track, 145770 cylinders
    Units = cylinders of 16065 * 512 = 8225280 bytes

       Device Boot      Start         End      Blocks   Id  System
    /dev/sdc1               1      145771  1170897919+  ee  EFI GPT

[root@test ~]# parted /dev/sdc print

    Model: LSI MR9361-8i (scsi)
    Disk /dev/sdc: 1199GB
    Sector size (logical/physical): 512B/512B
    Partition Table: gpt

    Number  Start   End     Size    File system  Name     Flags
     1      131kB   1199GB  1199GB  ext3         zfs
     9      1199GB  1199GB  8389kB               solaris

    Information: Don't forget to update /etc/fstab, if necessary.