SqlServer 2005 读书笔记 3 - raid

 Raid

Striple&Mirror

 

Raid0 - Striple

Raid1 - Mirror

Raid10 - Striple&Mirror

Raid5 - Striple&Parity

 

Performance&Capacity

                Read(R)          Write(R)    IO/Disk                    Capacity

Raid0       n                      n               IO/n                         t   

Raid1       2(split seek)    1(cache)    read/2+write            t/2

Raid10     n                      n/2            read/n+write*2/n     t/2

Raid5       n                      n/4            read/n+write*4/n     t*n/(n-1)

 

<10% write operation - raid5

>10% write opeateion - raid10

 

Parity for raid5

each write opearion involves 4 IO,sequences:

1.IO occurs to raid controller

2.Read the old data

3.Read the partiy data

4.Cal new parity bit - #2 xor #3

5.Write new data

6.Write new parity data