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Full Discussion: LUN Presentation
Operating Systems Linux Red Hat LUN Presentation Post 302632047 by mark54g on Saturday 28th of April 2012 11:28:25 PM
Old 04-29-2012
If you have a /dev/dm device, you HAVE presented the LUN. This is the multipath daemon's way of abstracting the multiple paths as one device.

That way, assuming you had /dev/sdb, sdc, sdd, sde as 4 paths to the same disk, you would use /dev/dm-0 as the path you choose, and if you lose /dev/sdc then you still have 3 active paths and no loss in access, but perhaps performance

(Besides, an EVA only allows access via one controller at a time until a failure causes it to switch controllers. It's really the "Speak and Spell" of SAN technology)

In the Command View EVA tool you present the device to the WWN(s) of the host (You did properly zone the switch, correct?)

After that, you should follow the instructions on this page:

Scan and Configure New LUNS on Redhat Linux (RHEL)

If you are using native multipathing, run multipath -ll

Make sure the system sees all the paths. You can also create a disk lable with e2label (That way, when you run blkid, you can see which devices correspond to which path, etc without multipath -ll)

Tutorial: e2label, fdisk, /etc/fstab, mount, linux rescue, rescue disk, CentOS should help you there.
 

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cmdisklock(1m)															    cmdisklock(1m)

NAME
cmdisklock - manage Serviceguard cluster lock devices. SYNOPSIS
cmdisklock check path cmdisklock [-f] reset path DESCRIPTION
cmdisklock is a tool to check the current state of a Serviceguard cluster lock device. It can also be used to reset the state of the clus- ter lock device. The need to reset the cluster lock device state could arise if the cluster lock device is replaced or becomes corrupt. A cluster lock device can be either an HP-UX LVM cluster lock or a cluster lock LUN device. HP-UX LVM cluster locks exist only on a disk in an LVM volume group. Cluster lock LUNs exist only on disks dedicated to cluster lock. cmdisklock is useful for checking either type of cluster lock and for re-initializing cluster lock LUN devices after a failure or corruption. NOTE To restore an HP-UX LVM cluster lock, use vgcfgrestore. cmdisklock will fail until vgcfgrestore is run, and cmdisklock is unnecessary as long as vgcfgbackup was done after the cluster lock was initialized. See the Managing Serviceguard manual for details. The syntax of the path option depends on the type of lock. For HP-UX LVM cluster lock disks, the syntax is VG:PV (for example: /dev/vglock:/dev/dsk/c0t0d2). For cluster lock LUN disks, the path is the disk device path. For example, /dev/sdd1 (on Linux) or /dev/dsk/c0t1d2 (on HP-UX). Options cmdisklock supports the following options: check Check the current state of the cluster lock device and report the results. reset Reset (initialize) the state of the cluster lock device. This operation should only be performed on a cluster lock LUN device. For HP-UX LVM cluster lock, use vgcfgrestore as documented in the Managing Serviceguard manual. After performing a reset, a check can be used to verify that the lock is cleared. EXAMPLES
If the cluster lock LUN device becomes corrupted and the cluster is up, messages like the following will appear in syslog. Mar 15 12:20:41 usb cmdisklockd[17599]: WARNING: Cluster lock LUN /dev/dsk/c0t1d2 is corrupt: bad label. Until this situation is cor- rected, a single failure could cause all nodes in the cluster to crash. Mar 15 12:20:41 usb cmdisklockd[17599]: After ensuring that all active nodes in the cluster have logged this message, run 'cmdisklock reset /dev/dsk/c0t1d2' to repair Mar 15 12:20:41 usb cmdisklockd[17599]: Cluster lock disk /dev/dsk/c0t1d2 is inaccessible Once the above messages appear in syslog on all running nodes, the following command will re-initialize the cluster lock LUN: ucd:/> cmdisklock reset /dev/dsk/c0t1d2 WARNING: Cluster lock LUN /dev/dsk/c0t1d2 is corrupt: bad label. Until this situation is corrected, a single failure could cause all nodes in the cluster to crash. After ensuring that all active nodes in the cluster have logged this message, run 'cmdisklock reset /dev/dsk/c0t1d2' to repair /dev/dsk/c0t1d2 is inaccessible Resetting cluster lock device /dev/dsk/c0t1d2 Cluster lock reset completed /dev/dsk/c0t1d2 is accessible cleared After the lock is restored, a message like the following appears in syslog: Mar 15 12:23:11 usb cmdisklockd[17599]: Cluster lock disk /dev/dsk/c0t1d2 is accessible WARNINGS
CAUTION For cluster lock LUN, reset is a potentially destructive operation. While cmdisklock checks for known volume manager and file system use (overridden by -f), it does not validate that the device to be reset is actually used by any cluster. If -f is used on the wrong device file, loss of data may result. CAUTION Care should be taken when doing a reset when the cluster is active as there is a remote possibility that the cluster will partition right when this command is run and both nodes could end up thinking they have successfully acquired the lock. To avoid this situation, make sure cmcld has logged a message in syslog on all running nodes saying the device is inaccessble, before performing a reset. Note that it is safe to run cmdisklock when the cluster is down. RETURN VALUE
cmdisklock returns the following values: 0 Successful completion. 1 The disk is inaccessible or is not recognized as a cluster lock. AUTHOR
cmdisklock was developed by HP. SEE ALSO
cmapplyconf(1m), cmviewcl(1m), vgcfgbackup(1m), vgcfgrestore(1m) Requires Optional Serviceguard Software cmdisklock(1m)
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