Promise Technology 2-Year Extended Warranty for VessR2000 RAID Head - Manual (Page 614)

587
Product Manual Technology Background
raid C
oNtrollers
RAID controller technology includes;
• “LUN Affinity” (below)
• “ALUA” (below)
• “Cache Policy” on page 588
• “Read Cache Policy” on page 588
• “Write Cache Policy” on page 589
• “Power Saving” on page 591
• “Capacity Coercion” on page 591
lun A
ffinity
Vess 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 101.
• Enable LUN Affinity. See “Making Controller Settings” on page 113 .
On subsystems with two RAID controllers, when Cache Mirroring is disabled, LUN Affinity is enabled automatically.
AluA
Vess 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 101.
• Enable LUN Affinity and ALUA. See “Making Controller Settings” on page 113 .