
4.8 The value of RAID 293
Chapter 4
the RAID set and is a simple logical XOR of each data block of each vol-
ume. This parity information is stored in place of data in a member of a
RAID5 set. Whereas RAID3 dedicates a drive for storing parity, RAID5
distributes the parity across all members of a disk. Locating the parity on a
single drive can quickly turn that drive into a hot spot where time is spent
waiting for the total write operation to complete.
When data must be read from a RAID5 volume, the performance and
access pattern of the disk drive is similar to a regular stripe set (RAID0).
The big difference comes when data must be written or updated ...