Specifications

Device Mapper Multipath I/O Configurations
Single Path on
Boot Up Does
Not Cause
Notification
If a server can access only a single path to the storage when the system is
loaded, there will be no notification of this problem. This can happen if a system
is rebooted where there is a physical path failure as noted above, but transient
path failures have also been observed. It is advised that any time a system is
loaded, the administrator should check that all paths to the storage are properly
configured, and if not, take actions to either repair any hardware problems or
reload the system to resolve a transient problem.
Device Mapper Multipath I/O Configurations
Protecting
Applications
and File
Systems That
Use Device
Mapper
Multipath
Devices
In order for LifeKeeper to operate with and protect applications or file systems that
use Device Mapper Multipath devices, the Device Mapper Multipath (DMMP)
Recovery Kit must be installed.
Once the DMMP Kit is installed, simply creating an application hierarchy that uses
one or more of the multipath device nodes will automatically incorporate the new
resource types provided by the DMMP Kit.
Multipath
Device
Nodes
To use the DMMP Kit, any file systems and raw devices must be mounted or
configured on the multipath device nodes rather than on the native /dev/sd* device
nodes. The supported multipath device nodes to address the full disk are /dev/dm-
#, /dev/mapper/<uuid>, /dev/mapper/<user_friendly_name> and
/dev/mpath/<uuid>. To address the partitions of a disk, use the device nodes for
each partition created in the /dev/mapper directory.
Use of SCSI-
3 Persistent
Reservations
The Device Mapper Multipath Recovery Kit uses SCSI-3 persistent reservations
with a "Write Exclusive" reservation type. This means that devices reserved by
one node in the cluster will remain read-accessible to other nodes in the cluster,
but those other nodes will be unable to write to the device. Note thatthis does
not meanthat you can expect to be able to mount file systems on those other
nodes for ongoing read-only access.
LifeKeeper uses the sg_persist utility to issue and monitor persistent reservations.
If necessary, LifeKeeper will install the sg_persist(8) utility.
SCSI-3 Persistent Reservations must be enabled on a per LUN basis when using
EMC Symmetrix (including VMAX) arrays with multipathing software and
LifeKeeper.
100Configuration