SHARKOON 5-Bay RAID-Station - Manual (Page 34)

5-bay raid station 34
11.7 R3 mode
Function:
The R3 mode requires a minimum of three drives to implement. The R3 mode adds fault
tolerance to drive striping by adding parity information to the data. R3 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 one drive. There are at least three
volumes to create a virtual R3 volume. The following example illustrates how the parity is
rotated from drive to drive.
Advantage/disadvantage:
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. When the offline drive comes back
online, the appliance begins a rebuild process immediately to restore data redundancy.
During this procedure the LED indications will notify you that a rebuild is in progress.
Notes:
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.
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