※ [本文转录自 SYSOP 看板] 作者: Ptt (杜奕瑾) 看板: SYSOP 标题: Re: 感谢站长！ 时间: Thu May 20 22:35:31 1999 ※ 引述《stevel (环游世界)》之铭言： : ※ 引述《Ptt (杜奕瑾)》之铭言： : : b. RAID5是一般大公司会用的 也是最好的方式 : : 但: : : 1. RAID5需要用到一倍HD : RAID 5 平均只有一颗 HD 是拿来放 parity 的，其他都是放 data， : 怎麽会多用到「一倍」的 HD 呢？ : 还是我会错意了？(要 construct RAID5 之时会用到「一倍」 HD) yea 是Ptt书读不精 误导大家 :) 谢谢stevel指正 RAID-1 才需要至少一倍的空间 RAID-5 只要多一颗parity的HD 不过 用做RAID的硬碟都要同一大小型号才好 现在的硬碟又不太适合 相关文件如下: RAID-0 RAID Level 0 is not redundant, hence does not truly fit the "RAID" acronym. In level 0, data is split across drives, resulting in higher data throughput. Since no redundant information is stored, performance is very good, but the failure of any disk in the array results in data loss. This level is commonly referred to as striping. RAID-1 RAID Level 1 provides redundancy by writing all data to two or more drives. The performance of a level 1 array tends to be faster on reads and slower on writes compared to a single drive, but if either drive fails, no data is lost. This is a good entry-level redundant system, since only two drives are required; however, since one drive is used to store a duplicate of the data, the cost per megabyte is high. This level is commonly referred to as mirroring. RAID-2 RAID Level 2, which uses Hamming error correction codes, is intended for use with drives which do not have built-in error detection. All SCSI drives support built-in error detection, so this level is of little use when using SCSI drives. RAID-3 RAID Level 3 stripes data at a byte level across several drives, with parity stored on one drive. It is otherwise similar to level 4. Byte-level striping requires hardware support for efficient use. RAID-4 RAID Level 4 stripes data at a block level across several drives, with parity stored on one drive. The parity information allows recovery from the failure of any single drive. The performance of a level 4 array is very good for reads (the same as level 0). Writes, however, require that parity data be updated each time. This slows small random writes, in particular, though large writes or sequential writes are fairly fast. Because only one drive in the array stores redundant data, the cost per megabyte of a level 4 array can be fairly low. RAID-5 RAID Level 5 is similar to level 4, but distributes parity among the drives. This can speed small writes in multiprocessing systems, since the parity disk does not become a bottleneck. Because parity data must be skipped on each drive during reads, however, the performance for reads tends to be considerably lower than a level 4 array. The cost per megabyte is the same as for level 4. --

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