RAID levels 4 through 6 make use of an independent access technique, where each member disk operates independently, so that separate I/O request can be satisfied in parallel.
Data stripings are used in this scheme also, but the data strips are relatively large for RAID levels 4 through 6.
With RAID 4, a bit-by-bit parity strip is calculated across corresponding strips on each data disks, and the parity bits are stored in the corresponding strip on the parity disk.
RAID 4 involves a write penalty when an I/O write request of small size is occurred. Each time a write occurs, update is required both in user data and the corresponding parity bits.
RAID level 5 is similar to RAID 4, only the difference is that RAID 5 distributes the parity strips across all disks.
The distribution of parity strips across all drives avoids the potential I/O bottleneck.