topic Re: Redhat Linux multipathing question in Operating System - Linux

Redhat Linux multipathing question

Dineshkumar Surpur — Mon, 17 Jan 2005 14:28:43 GMT

Hi,

We are running RedHat Enterprise Linux 3.0 update 4 connected to a SAN storage and using QLogic Fibre Channel HBA on the host server. We are evaluating multipath solutions and have to use active/active multipathing. Veritas VxVM is expensive and ruled out. I am looking for using LVM or EVMS which i beleive uses MP driver. Is is not MP driver is active/passive ? Does anybody recommend what i need to do to get active/active multipathing using LVM or EVMS or any other solution for active/active multipathing on Linux? Any documents or links will be very helpful .

Thanks.

Re: Redhat Linux multipathing question

Huc_1 — Tue, 18 Jan 2005 01:48:57 GMT

I guess a good starting point for EVMS would be
http://evms.sourceforge.net/

Jean-Pierre

Re: Redhat Linux multipathing question

Serviceguard for Linux — Tue, 18 Jan 2005 16:13:37 GMT

LVM oes not have multipathing built in. LVM2 uses DM which does have MP capability. Either way, I'm 99% sure that DM does not have active/active capability.

What storage are you using - not all storage would provide any performance benefit with active/active connections.

Re: Redhat Linux multipathing question

Dineshkumar Surpur — Tue, 18 Jan 2005 19:36:22 GMT

we are using 3par storage which provides performance benefits using active/active multipathing. SuSE provided Device Mapper on its 2.6.10 kernel which is actice/active anything like that on RedHat 2.4 kernel to acheive active/active MP

Re: Redhat Linux multipathing question

Dineshkumar Surpur — Tue, 25 Jan 2005 18:41:47 GMT

I have tried LVM present on RedHat Enterprise Edition 3 Update 4.

# rpm -qa lvm
lvm-1.0.8-9

Once the path is faulty the path never comes back to active or sparse by itself and one has to do remove the device and add back the device recreating the array for the path to be used again.

Ex:

# mdadm -C /dev/md0 --level=multipath --raid-devices=2 /dev/sdb1 /dev/sdc1

where /dev/sdb1 and /dev/sdc1 are paths to the same storage volume.

say if sdb1 becomes faulty (ex: Fibre Cable pull test) once the path and the device have come back the mdadm doesn't detect the path has come active and one has to remove the add the device back ex: sdb1 in the followig example to change its state from faulty.

# mdadm /dev/md0 -r /dev/sdb1
# mdadm /dev/md0 -a /dev/sdb1

Does anybody know of a way for mdadm to auto detect the path has come back and change the mode from faulty to active or sparse ?

BTW LVM is active/passive since it depends on mdadm is active/passive and LVM2 in 2.6 will use device mapper which is active/active.