Advantages; Disadvantage - HP 345646-001 - StorageWorks NAS 2000s External Storage Server Administration Manual

Storage Management Overview
This technology allows the safe deployment of large capacity disk drives and the creation of
very large storage volumes without expensive overhead to protect business critical data. This
technology provides more flexibility in responding to drive failures without the fear of costly
server downtime.
Advance Data Guarding protects against multiple disk failures, while requiring the capacity of
two drives in an array of up to 56 disk drives to be set aside for dual sets of distributed parity
data. It provides data protection greater than RAID 5, and also has the capacity utilization
efficiency similar to RAID 5.

Advantages

Disadvantage

The table below summarizes the important features of the different kinds of RAID supported
by the Smart Array controllers. The decision chart in the following table may help determine
which option is best for different situations.
Table 3: Summary of RAID Methods
Usable drive space
formula
Minimum number of
hard drives
Maximum number of
hard drives
Tolerant of single hard
drive failure?
Tolerant of multiple
simultaneous hard drive
failure?
52
High read performance
High data availability-any two drives can fail without loss of critical data
Relatively low write performance (lower than RAID 5), due to the need for two sets of
parity data
Striping (no
n
1
N/A
No
No
RAID 0 RAID 1+0
Mirroring
fault
tolerance)
n/2
2
N/A
Yes
For RAID
1+0, if the
failed drives
are not
mirrored to
each other
RAID 5 RAID ADG
Distributed Advanced
Data Data
Guarding Guarding
(n-1)/n (n-2)/n
3 4
14 56
Yes Yes
No Yes
(two drives
can fail)
NAS 2000s Administration Guide