具有最高的安全性，但磁盘空间利用率只有50%的是（40）。
- A.RAID0
- B.RAID1
- C.RAID3
- D.RAID5
正确答案及解析
正确答案
解析
独立冗余磁盘阵列（Redundant Array of Independent Disks，RAID）技术是一种用多个较小的磁盘替换单一的大容量磁盘，并通过合理地在多个磁盘上存放数据以提高系统的I/O性能。
RAID中共分以下几个级别：
（1）RAID 0级（无冗余和无校验的数据分块）：具有最高的I/O性能和最高的磁盘空间利用率，但系统的故障率高，属于非冗余系统。
（2）RAID 1级（磁盘镜像阵列）：由磁盘对组成，每一个工作盘都有其对应的镜像盘，上面保存着与工作盘完全相同的数据拷贝，具有最高的安全性，但磁盘空间利用率只有50%。
（3）RAID 2级（采用纠错海明码的磁盘阵列）：采用了海明码纠错技术，用户需增加校验盘来提高可靠性，在大量数据传输时，I/O性能较高，但不利于小批量数据传输。
（4）RAID 3级和RAID 4级（采用奇偶校验码的磁盘阵列）：把奇偶校验码存放在一个独立的校验盘上。如果有一个盘失效，其数据可以通过对其他盘上的数据进行异或运算得到。读数据很快，但写入数据时要计算校验位，速度较慢。
（5）RAID 5级（无独立校验盘的奇偶校验码磁盘阵列）：没有独立的校验盘，校验信息分布在组内所有盘上，对于大批量和小批量数据的读写性能都很好。
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