A disk system is to be constructed using some number of iden

A disk system is to be constructed using some number of identical disk drives each of which can store up to T terabytes of data. A large database of size 4×T terabytes is to be stored on the disk system. What is the minimum total number of disks that would be required for the system if the disk system is a:

a) RAID4 system?

b) RAID5 system?

c) RAID6 system?

d) RAID1 system?

e) RAID0 system?

Solution

a) RAID4 system?: This consists of the block level striping, and an extra dedicated parity disk. Therefore, it requires just an extra disk for parity. So, the answer is: 5 disks.

b) RAID5 system?: This consists of the block level striping with distributed parity. Everything else remains the same. Therefore, it requires just an extra disk for parity. So, the answer is again: 5 disks.

c) RAID6 system?: This system extends the RAID5 by adding another parity block. therefore, every block will have 2 extra parity blocks. Therefore, it requires 2 extra disks for parity. So, the answer is: 6 disks.

d) RAID1 system?: The consists an exact copy of the original data. A mirror of the whole data. Therefore, to store the data of 4 x T terabytes, the number of extra disks required is again 4 more disks. So, the answer is: 8 disks.

e) RAID0 system?: This is the most unreliable one, and its just for a little bit of performance improvement. No extra disks are required, and no redundant data will be stored in this system. So, the answer is: 4 disks