First Virtual Communications Voyager 3000 - Manual (Page 20)

Voyager 3000 User Guide
1-10
RAID 3
Block Striping with Dedicated Parity - Data is broken into logical blocks, the size of a SCSI
disk block, and striped across several drives. One drive is dedicated to parity. In the event of
failure, original data is re-generated from the parity information.
Table 1-7 RAID 3 layout
Drive 0 Drive 1 Drive 2 Drive 3 Drive 4
A0 A1 A2 A3 P
A4 B0 B1 B2 P
B3 B4 C0 C1 P
C2 C3 C4 D0 P
RAID 5
Multiple Block Striping with Distributed Parity - Sets a given number of logical blocks as a
unit for striping across several drives. For small read/write operations, one drive may be
activated for improved small record access speed. In this case we can process multiple I/O
requests simultaneously. Parity information is interleaved across the drive array. In the event
of failure, original data is regenerated from the parity information.
Table 1-8 RAID 5 layout
Drive 0 Drive 1 Drive 2 Drive 3 Drive 4
A0-A1 A2-A3 A4-B0 B1-B2 P
B3-B4 C0-C1 C2-C3 P C4-D0
D1-D2 D3-D4 P E0-E1 E2-E3
E4-F0 p F1-F2 F3-F4 G0-G1
Required Number of Drives and Net Capacity
The following table gives a summary of the minimum number of drives required and the
capacity available for the different types of RAID operation:
Table 1-9 Minimum drives necessary for a RAID set
OPERATION MIN. DRIVES
REQUIRED
CAPACITY
AVAILABLE
RAID 0 2 T
RAID 1 2 T / 2
RAID 0 + 1 4 T / 2
RAID 3 3 T x (n - 1) / n
RAID 5 3 T x (n - 1) / n
T = Sum of the capacity of all connected drives
n = Number of connected drives