User`s manual

drive. There are at least 3 members to a virtual R3 volume. The following example illustrates how the parity is
rotated from drive to drive.
The R3 MODE uses less capacity for protection and is the preferred method to reduce the cost per megabyte for
larger installations.
In exchange for low overhead necessary to implement protection, the R3 MODE degrades performance for all
write operations. The parity calculations for R3 MODE may result in write performance that is somewhat slower
than the write performance to a single drive.
The resulting storage capacity of the virtual R3 volume will be four times of the smallest drive.
If one drive fails, the virtual R3 volume is still usable, but it is in a vulnerable state because its mirrored hard drive
is inaccessible. When the offline drive comes back online, the appliance begins a rebuild process immediately to
restore data redundancy. A message appears in the LED indicator to notify you that a rebuild is in progress.
Although the volume remains available during the rebuild process, the volume is susceptible to data loss through
damage to the remaining drive until redundancy is restored at the end of the rebuild and verification process. Host
access takes precedence over the rebuild process. If you continue to use the virtual R3 volume during the rebuild,
the rebuild process will take a longer time to complete, and the host data transfer performance will also be
affected.
2.1.8 R5 MODE
The R5 MODE storage policy requires a minimum of 3 drives to implement. The R5 MODE adds fault tolerance to
drive striping by including parity information with the data. R5 MODE dedicates the equivalent of one drive for
storing parity stripes. The data and parity information is arranged on the drive array so that parity is written to all
drives. There are at least 3 members to a virtual R5 volume. The following example illustrates how the parity is
rotated from drive to drive.
AES-S3504UE User’s Manual Ver. 091015
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