LSI 500 Manuel D’Utilisation
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.
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.
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.