※ [本文轉錄自 SYSOP 看板]
作者: Ptt (杜奕瑾) 看板: SYSOP
標題: Re: 感謝站長！
時間: Thu May 20 22:35:31 1999
※ 引述《stevel (環游世界)》之銘言：
: ※ 引述《Ptt (杜奕瑾)》之銘言：
: : b. RAID5是一般大公司會用的 也是最好的方式
: : 但:
: : 1. RAID5需要用到一倍HD
: RAID 5 平均只有一顆 HD 是拿來放 parity 的，其他都是放 data，
: 怎麼會多用到「一倍」的 HD 呢？
: 還是我會錯意了？(要 construct RAID5 之時會用到「一倍」 HD)
yea 是Ptt書讀不精 誤導大家 :)
謝謝stevel指正
RAID-1 才需要至少一倍的空間
RAID-5 只要多一顆parity的HD
不過
用做RAID的硬碟都要同一大小型號才好
現在的硬碟又不太適合
相關文件如下:
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.
--
※ 發信站: 批踢踢實業坊(ptt.twbbs.org)
◆ From: sevenup.csie.nt
--
※ 發信站: 批踢踢實業坊(ptt.twbbs.org)
◆ From: h227.s79.ts30.h