Linux – Number of device listed with multipath -ll

linuxmultipath

Hope i am not wasting anyone´s time, so apologies to all should that be the case with this question.

it is the first time i am playing with multipath, manged to setup multipath on a RHL5, the setup comprises of the following:

RHL5 Server has 2 x HBA – HBA1 Port1 connects to Fiber Switch 1 & HBA2 port1 connects to fiber switch 2

NETAPP FAS2040 Storage with one HBA with 2 ports, port 1 connects to Fiber Switch 1 & port 2 connects to Fiber Switch 2.

multipath -ll command show the following:

[root@nonameserver /]# multipath -ll
mpath0 (360a98000323766586b24422f6735626c) dm-2 NETAPP,LUN
[size=149G][features=1 queue_if_no_path][hwhandler=0]
\_ round-robin 0 [prio=2][active]
 \_ 4:0:0:0 sda 8:0   [active][ready]
 \_ 2:0:0:0 sdb 8:16  [active][ready]

My question is why is there two devices /dev/sda & /dev/sdb? on the storage there is only one LUN setup for the host.

Thank you all.

Best Answer

The /dev/sda device is the target LUN as seen through one HBA, the /dev/sdb device is the same LUN seen through the other HBA. That's how it works - different controllers means different devices. As the other answer you commented about notes, do not use sda or sdb - use the multipath device (/dev/mpath0).

Related Solutions

Ubuntu – How to dismount SAN device – multipath on Ubuntu

I've found device being using in /etc/exports for sharing to nfs clients. After running exportfs -rv, removing device from smbd.conf (restarting samba) and removing device from /etc/fstab i was able to unmount device umount /srv/media.

I've also did:

root@fs2:/# multipath -ll
media (360060160c8101f00d25370be50a6df11) dm-0 DGC     ,RAID 5        
[size=2.8T][features=1 queue_if_no_path][hwhandler=1 emc]
\_ round-robin 0 [prio=1][active]
 \_ 3:0:0:0 sda 8:0   [active][ready]
\_ round-robin 0 [prio=0][enabled]
 \_ 2:0:0:0 sdb 8:16  [active][ready]
root@fs2:/# multipath -F
root@fs2:/# multipath -ll

Finally (where sda and sdb are taken from multipath):

root@fs2:/# echo 1 > /sys/block/sda/device/delete
root@fs2:/# echo 1 > /sys/block/sdb/device/delete

Which brings these messages in dmesg:

[9847487.812391] sd 3:0:0:0: emc: Detached
[9847491.460307] sd 2:0:0:0: emc: Detached

Which seems to finally dismount device. Hope someone finds this useful :-)

Linux – /dev/disk/by-id/scsi-* links pointing to sdX instead of multipath device

From the documentation:

In SUSE Linux Enterprise Server 10, the kpartx software is used in the /etc/init.d/boot.multipath to add symlinks to the /dev/dm-* line in the multipath.conf configuration file for any newly created partitions without requiring a reboot. This triggers udevd to fill in the /dev/disk/by-* symlinks.

So, I would

Check whether boot.multipath was run on the second server
Check that udev is configured identically on both servers
Check that udevd is running on the second server

If all of that is true, you could try running kpartx -a on the multipath devices to see if the entries in /dev/disk/by-id/ are updated.

After you straighten this out, you still need to edit lvm.conf. Again, from the documentation:

By default, LVM2 does not recognize multipathed devices. To make LVM2 recognize the multipathed devices as possible physical volumes, you must modify /etc/lvm/lvm.conf. It is important to modify it so that it does not scan and use the physical paths, but only accesses the multipath I/O storage through the multipath I/O layer. If you are using user-friendly names, make sure to specify the path so that it scans only the device mapper names for the device (/dev/disk/by-id/dm-uuid-.-mpath-.) after multipathing is configured.

Best Answer

Related Solutions

Ubuntu – How to dismount SAN device – multipath on Ubuntu

Linux – /dev/disk/by-id/scsi-* links pointing to sdX instead of multipath device

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