Product manual

Chapter 7: Technology Background
361
RAID Controllers
RAID controller technology includes;
• LUN Affinity (page 361)
• ALUA (page 361)
• Cache Policy (page 362)
• Preferred Controller ID (page 364)
• Power Saving (page 364)
• Capacity Coercion (page 364)
LUN Affinity
VTrak subsystems with dual RAID controllers include a LUN Affinity feature.
Normally, either controller can access all logical drives. LUN Affinity enables you
to specify which controller can access each logical drive. Use this feature to
balance the load of your logical drives between the two controllers.
To use LUN Affinity you must:
• Have two RAID controllers in the subsystem.
• Set the redundancy type to Active-Active.
See “Making Subsystem Settings” on page 77 or page 211.
• Enable LUN Affinity.
See “Making Controller Settings” on page 86 or page 216.
On subsystems with two RAID controllers, when Cache Mirroring is disabled,
LUN Affinity is enabled automatically.
ALUA
VTrak supports Asymmetric Logical Unit Access (ALUA) on Linux OSes. ALUA is
a multhipathing tool. It enables an initiator (your host PC or server) to discover
target port groups that provide a common failover/failback behavior for your
LUNs. ALUA enables the host to see which paths are in an optimal state and
which are not.
To use ALUA you must:
• Have two RAID controllers in the subsystem.
• Set the redundancy type to Active-Active.
See “Making Subsystem Settings” on page 77 or page 211.
• Enable LUN Affinity and ALUA.
See “Making Controller Settings” on page 86 or page 216.
For more information, see “Appendix C: Multipathing on Linux” on page 471.