Linux Multipath configuration

[Mike Hedderly]

I have two DL380's in a redhat cluster. I have just installed a two MSA1000 controllers in a Active/Standby configuration, with 2 SAN switches. The DL380's have a dual port fibre card. The problem I have is that if the right hard MSA1000 starts first the disks are /dev/sda1,2,3,4 and if the left hand MSA1000 starts they are /dev/sdb1,2,3,4. So I thought I would created a MD device. The problem is that I can create MD0 as /dev/sda1 /dev/sdb1 but it tells me that /dev/sdb1 is not there.

mdadm -C /dev/md1 --level=raid0 --raid-devices=2 /dev/sda1 /de
v/sdb1
mdadm: /dev/sda1 appears to contain an ext2fs file system
size=16032K mtime=Thu Jan 1 00:00:00 1970
mdadm: Cannot open /dev/sdb1: No such device or address
mdadm: create aborted

any ideas ?

[Ivan Ferreira]

I think that the right command is:

mdadm -C /dev/md1 --level=multipath --raid-devices=2 /dev/sda1 /dev/sdb1

[Mike Hedderly]

Still gives the error

mdadm: Cannot open /dev/sdb1: No such device or address

[Ivan Ferreira]

If you do fdisk -l, can you see both devices /dev/sda and /dev/sdb?

You can also try:

mknod /dev/sdb b 8 16

You can also run hp_rescan -a if you installed fibreutils. You can try with the rescan-scsi-bus.sh script also.

[Mike Hedderly]

If I do fdisk, i do not see /dev/sda or /dev/sdb

[Ivan Ferreira]

What about if you use parted?

parted /dev/sda print
parted /dev/sdb print

Remember to try to create the devices if you don't get any output.

[Mike Hedderly]

I think the problem is that there is no partition table for /dev/sda

if I try and used parted to create one it gives an error unbale to open device


[root@ralph root]# parted /dev/sda print
Error: Unable to open /dev/sda - unrecognised disk label.
Information: Don't forget to update /etc/fstab, if necessary.

[root@ralph root]# parted /dev/sdb print
Disk geometry for /dev/sdb: 0.000-208390.781 megabytes
Disk label type: msdos
Minor Start End Type Filesystem Flags
1 0.031 15.688 primary ext3 boot
2 15.688 31.376 primary ext3
3 31.377 89996.945 primary ext3
4 89996.946 149997.524 primary ext3
Information: Don't forget to update /etc/fstab, if necessary.

[Ivan Ferreira]

Remember that they are the same device, if you access through sda or sdb, you should access the same device. Do not try to create the partition table again. But you are able to se sdb, I don't know why mdadm gives the error.

[Ivan Ferreira · Accepted solution]

Probably if you install the multipath hba driver you won't have this problem.

[Anthony Martin_1]

Hi Mike,
What you are trying to do will not work.
In order to create a RAID device, you must have two active paths to the storage subsystem. The MSA1000 only has one active path and does not present the other path to any server unless the active controller fails for some reason.
When you boot a Linux server, you will see one MSA1000 controller changing to the Active controller when being probed by the QLogic card attached to it. The other controller becomes a Standby controller.
With two cards in the server, each controller will become active at some stage, but not both controllers at the same time. Therefore paths will lost by the server.
Your configuration would work in a Active/Active controller SAN, eg MSA1500 or EVA system.

My suggestion for you is to use the QLogic driver with the failover option.

Hope this helps
Anthony

[Mike Hedderly]

That seems to have done the trick. I have configured the qloic drive in MSA failover mode and only one MSA1000 and one disk /dev/sda is presented to the operating system.. Failover of the controller takes around 20 seconds.

[Uwe Zessin]

> Your configuration would work in a Active/Active controller SAN, eg MSA1500 or EVA system.

Sorry, but the MSA1000/MSA1500cs is not Active/Active, yet. And EVA3000/5000 are not Active/Active until VCS V4.