RAID5没有单独指定的奇偶盘, 而是交叉地存取数据及奇偶校验信息于所有磁盘上。 在RAID5上, 读/写指针可同时对阵列设备进行操作, 提供了更高的数据流量。 RAID5更适合于小数据块,随机读写的数据。RAID 3与RAID5相比, 重要的区别在于RAID 3每进行一次数据传输,需涉及到所有的阵列盘。而对于RAID5来说, 大部分数据传输只对一块磁盘操作, 可进行并行操作。在RAID5中有“写损失”, 即每一次写操作,将产生四个实际的读/写操作, 其中两次读旧的数据及奇偶信息, 两次写新的数据及奇偶信息。
RAID 5: Independent Data disks with distributed parity blocks
Characteristics/Advantages
1. Highest Read data transaction rate
2. Medium Write data transaction rate
3. Low ratio of ECC (Parity) disks to data disks means high efficiency
4. Good aggregate transfer rate
Disadvantages
1. Disk failure has a medium impact on throughput
2. Most complex controller design
3. Difficult to rebuild in the event of a disk failure (as compared to RAID level 1)
4. Individual block data transfer rate same as single disk
Recommended Applications
1. File and Application servers
2. Database servers
3. WWW, E-mail, and News servers
4. Intranet servers
5. Most versatile RAID level
Each entire data block is written on a data disk; parity for blocks in the same rank is generated on Writes, recorded in a distributed location and checked on Reads.
RAID Level 5 requires a minimum of 3 drives to implement
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[...] 与RAID 5相比,增加了第二个独立的奇偶校验信息块。 [...]