Consider the following points when you plan Solaris Volume Manager configurations:
Local volume names – The name of each local Solaris Volume Manager volume on which a global-devices file system, /global/.devices/node@nodeid, is mounted must be unique throughout the cluster. Also, the name cannot be the same as any device-ID name.
Dual-string mediators – Each disk set configured with exactly two disk strings and mastered by exactly two nodes must have Solaris Volume Manager mediators configured for the disk set. A disk string consists of a disk enclosure, its physical disks, cables from the enclosure to the node or nodes, and the interface adapter cards. Observe the following rules to configure dual-string mediators:
You must configure each disk set with exactly two nodes that act as mediator hosts.
You must use the same two nodes for all disk sets that require mediators. Those two nodes must master those disk sets.
Mediators cannot be configured for disk sets that do not meet the two-string and two-host requirements.
See the mediator(7D) man page for details.
/kernel/drv/md.conf settings – SPARC: On the Solaris 9 OS, Solaris Volume Manager volumes that are used by each disk set are created in advance, at reconfiguration boot time. This reconfiguration is based on the configuration parameters that exist in the /kernel/drv/md.conf file.
With the Solaris 10 release, Solaris Volume Manager has been enhanced to configure volumes dynamically. You no longer need to edit the nmd and the md_nsets parameters in the /kernel/drv/md.conf file. New volumes are dynamically created, as needed.
All cluster nodes must have identical /kernel/drv/md.conf files, regardless of the number of disk sets that are served by each node. Failure to follow this guideline can result in serious Solaris Volume Manager errors and possible loss of data.
md_nsets – The md_nsets field defines the total number of disk sets that can be created for a system to meet the needs of the entire cluster. Set the value of md_nsets to the expected number of disk sets in the cluster plus one additional disk set. Solaris Volume Manager software uses the additional disk set to manage the private disks on the local host.
The maximum number of disk sets that are allowed per cluster is 32. This number allows for 31 disk sets for general use plus one disk set for private disk management. The default value of md_nsets is 4.
nmd – The nmd field defines the highest predicted value of any volume name that will exist in the cluster. For example, if the highest value of the volume names that are used in the first 15 disk sets of a cluster is 10, but the highest value of the volume in the 16th disk set is 1000, set the value of nmd to at least 1000. Also, the value of nmd must be large enough to ensure that enough numbers exist for each device–ID name. The number must also be large enough to ensure that each local volume name can be unique throughout the cluster.
The highest allowed value of a volume name per disk set is 8192. The default value of nmd is 128.
Set these fields at installation time to allow for all predicted future expansion of the cluster. To increase the value of these fields after the cluster is in production is time consuming. The value change requires a reconfiguration reboot for each node. To raise these values later also increases the possibility of inadequate space allocation in the root (/) file system to create all of the requested devices.
At the same time, keep the value of the nmdfield and the md_nsets field as low as possible. Memory structures exist for all possible devices as determined by nmdand md_nsets, even if you have not created those devices. For optimal performance, keep the value of nmd and md_nsets only slightly higher than the number of volumes that you plan to use.