Comparing Raid Adg To Other Raid Methods - Compaq 166207-B21 - Smart Array 5302/32 RAID Controller Reference Manual

Overview of RAID ADG
Theoretically, RAID ADG can support a logical volume that spans over 200 hard
drives without any great risk of data loss. However, currently existing array
controllers and storage systems support no more than 14 drives per channel. Thus, the
largest obtainable logical volume, using a 4-channel controller, spans 56 hard drives.

Comparing RAID ADG to Other RAID Methods

Table 1-1 summarizes the most important features of the different RAID methods
that are supported by Compaq array controllers. For more detailed information, refer
to the user guide for the Smart Array controller that is installed in the system.
Table 1-1: Comparison of RAID Methods
Alternative name
Usable drive space*
Usable drive space
formula
Minimum number of
physical drives
Tolerates failure of
one physical drive?
Tolerates
simultaneous failure
of more than one
physical drive?
Read performance
Write performance
Relative cost
*Values for usable drive space are calculated with these assumptions: (1) All physical drives in the
array have the same capacity; (2) Online spares are not used; (3) No more than 14 physical drives
are used per array for RAID 5; (4) No more than 56 drives are used with RAID ADG.
1-2
RAID 0 RAID 1+0
Striping (no Mirroring
fault tolerance)
100% 50%
n n/2
1 2
No Yes
No Only if no two
failed drives are
in a mirrored pair
High High
High Medium
Low High
Compaq Advanced Data Guarding Option Software Reference Guide
RAID 5 RAID ADG
Distributed Advanced Data
Data Guarding Guarding
67% to 93% 50% to 96%
(n-1)/n (n-2)/n
3 4
Yes Yes
No Yes
High High
Low Low
Medium Medium