topic Re: SAN mounts connection problem in Operating System - Linux

SAN mounts connection problem

Fadia Almarei — Tue, 03 Nov 2009 09:40:48 GMT

Dear All

i have RHEL AS 4.8 server connected to DMX4 EMC SAN storage through dual switches and dual fibre cards and dual connections, if anyone of these connections lost these file systems will be mount in read only mode, how to change this option to be mounted as a read/write mode, as in hp-ux , i hear that tune2fs could do this , but i do not get the exact suitable option , kindly advice.

BR;

Re: SAN mounts connection problem

Matt Palmer_2 — Tue, 03 Nov 2009 11:01:39 GMT

HI, do you have any MPIO drivers and DM in place. These should be able to manage the loss of multiple paths to your SAN devices, without placing the fs in readonly mode

hope that helps

regards

Matt

Re: SAN mounts connection problem

Fadia Almarei — Tue, 03 Nov 2009 11:05:52 GMT

we have powerpath for EMC , but file systems mounted in read only mode if any connection problem happened.

Re: SAN mounts connection problem

Matti_Kurkela — Tue, 03 Nov 2009 12:27:25 GMT

Filesystems are mounted in read-only mode because an filesystem error has been detected. To get the filesystems back to read/write mode, you must unmount the filesystem, run fsck on it, and then you can mount it normally.

The system remembers that an error has been detected on a filesystem and will not let you mount it read/write until you run a fsck on that filesystem.

The root cause of your read-only problem is a failure of your multipath configuration.

If you are familiar with PowerPath in HP-UX, be aware that works very differently in Linux. You *must* use the /dev/emcpower* device names to get the benefit of PowerPath multipathing: if you use /dev/sd* devices, PowerPath is completely bypassed and it cannot help you when a path fails.

If you use traditional partitions, are the disks mounted using /dev/emcpower* device names?

If you use LVM, does the command

vgdisplay -v | grep "PV Name"

list /dev/emcpower* device names for all SAN PVs?
(If you haven't already done so, you may have to write a custom filter statement in /etc/lvm/lvm.conf to make the LVM use /dev/emcpower* devices and ignore the respective /dev/sd* devices.)

MK

Re: SAN mounts connection problem

Fadia Almarei — Tue, 03 Nov 2009 12:52:46 GMT

i already user powerpath device name , but still when i faced any problem it will be mounted as read-only ,and also i use LVM in configuring mount points any suggestion

Re: SAN mounts connection problem

Matt Palmer_2 — Tue, 03 Nov 2009 12:55:40 GMT

Hi,

which FC HBAs are you using? I have had problems with the FC adapter trying to manage the failover instead of MPIO when using Qlogic cards.

regards

Matt

Re: SAN mounts connection problem

Fadia Almarei — Tue, 03 Nov 2009 12:59:44 GMT

i have emulex HBA's

Re: SAN mounts connection problem

Matt Palmer_2 — Tue, 03 Nov 2009 13:07:04 GMT

Hi,

have you checked in the logs that the powerpath licence doesnt have an issue. I found the following resource on the web:

http://blog.thilelli.net/post/2009/02/09/Comparison:-EMC-PowerPath-vs-GNU/Linux-dm-multipath

"Keep in mind that without purchasing an appropriate EMC license, PowerPath can only be used in failover mode (active-passive mode). Multiple paths accesses are not supported in this case: no round-robin, and no I/O load balancer for example."

regards

Matt

Re: SAN mounts connection problem

Matti_Kurkela — Tue, 03 Nov 2009 14:37:01 GMT

Even the failover mode should have prevented errors when one SAN connection was lost.

Have you verified that PowerPath really can access the LUNs through both fibre cards?

What does "powermt display dev=all" say?

MK