同RAID2, RAID3一样, RAID4, RAID5也同样将数据条块化并分布于不同的磁盘上, 但条块单位为块或记录。 RAID4使用一块磁盘作为奇偶校验盘, 每次写操作都需要访问奇偶盘, 成为写操作的瓶颈。 在商业应用中很少使用。
RAID 4: Independent Data disks with shared Parity disk
Characteristics/Advantages
1. Very high Read data transaction rate
2. Low ratio of ECC (Parity) disks to data disks means high efficiency
3. High aggregate Read transfer rate
Disadvantages
1. Quite complex controller design
2. Worst Write transaction rate and Write aggregate transfer rate
3. Difficult and inefficient data rebuild in the event of disk failure
4. Block Read transfer rate equal to that of a single disk
Each entire block is written onto a data disk. Parity for same rank blocks is generated on Writes, recorded on the parity disk and checked on Reads.
RAID Level 4 requires a minimum of 3 drives to implement
