LSI MegaRAID Express 500 - Manual (Page 35)

Chapter 3 RAID Levels 21
RAID 3
RAID 3 provides disk striping and complete data redundancy though a dedicated parity
drive. The stripe size must be 64 KB if RAID 3 is used. RAID 3 handles data at the block
level, not the byte level, so it is ideal for networks that often handle very large files, such
as graphic images. RAID 3 breaks up data into smaller blocks, calculates parity by
performing an exclusive-or on the blocks, and then writes the blocks to all but one drive
in the array. The parity data created during the exclusive-or is then written to the last
drive in the array. The size of each block is determined by the stripe size parameter,
which is set during the creation of the RAID set.
If a single drive fails, a RAID 3 array continues to operate in degraded mode. If the failed
drive is a data drive, writes will continue as normal, except no data is written to the failed
drive. Reads reconstruct the data on the failed drive by performing an exclusive-or
operation on the remaining data in the stripe and the parity for that stripe. If the failed
drive is a parity drive, writes will occur as normal, except no parity is written. Reads
retrieve data from the disks.
Uses Best suited for applications such as graphics, imaging, or
video that call for reading and writing huge, sequential
blocks of data.
Strong Points Provides data redundancy and high data transfer rates.
Weak Points The dedicated parity disk is a bottleneck with random I/O.
Drives Three to 15
Cont’d