American Megatrends MegaRAID Express 500 - Manual (Page 36)

MegaRAID Express 500 Hardware Guide 22
RAID 3, Continued
RAID 5 vs RAID 3 You may find that RAID 5 is preferable to RAID 3, even for applications
characterized by sequential reads and writes, because MegaRAID Express 500
has very robust caching algorithms.
The benefits of RAID 3 disappear if there are many small I/O operations
scattered randomly and widely across the disks in the logical drive. The RAID 3
fixed parity disk becomes a bottleneck in such applications. For example: The
host attempts to make two small writes and the writes are widely scattered,
involving two different stripes and different disk drives. Ideally both writes
should take place at the same time. But this is not possible in RAID 3, since the
writes must take turns accessing the fixed parity drive. For this reason, RAID 5
is the clear choice in this scenario.