Specifications

RAIDs
Chapter 4 Storage Configuration & Expansion 31
would configure one of the drives as a hot spare. The following table summarizes
the advantages and disadvantages of each type of RAID:
RAID Groups
Two RAIDs can be grouped together to neatly resolve a number of capacity issues.
For example, a volume on one RAID nearing full utilization can be expanded using
spare capacity on another RAID. The ability to grow volumes beyond the capacity
of a single RAID allows administrators to expand a volume without reconfiguring
RAIDs and allows users to continue working as usual with no interruption.
Consider the following scenarios:
• Adding a Snap Disk Expansion Array —
In a common scenario, a Snap Server
4500 configured as a RAID 5 is nearing full utilization. The administrator decides
to add a Snap Disk 10 expansion array, which comes preconfigured as a RAID 5.
The administrator groups the RAID from the expansion array with the existing
RAID on the 4500, and then expands the size of the original volumes using the
new storage from the expansion array.
• Adapting to Unforeseen Requirements —
A Snap Server 14000 is originally
configured by an administrator with two separate RAIDs, each with its own hot
spare. Usage on the first RAID is higher than expected and lower on the second
RAID. By combining the RAIDs, the administrator can expand the volume from
the first raid using the capacity of the second.
Local and Global Hot Spares
A hot spare is a disk drive that can automatically replace a damaged drive in a RAID
1 or 5. Designating a disk drive as a hot spare helps ensure that data is available at
all times. If one disk drive in a RAID fails or is not operating properly, the RAID
Comparative Advantages of RAID Types
Features RAID 0 RAID 1 RAID 5
Data Loss Risk Highest Lowest Low
Write Access Speeds Fastest Slower Faster
Usable Capacity Highest Lowest High
Disks Required 1 or more 2 or more 3 or more
Supports Hot Spares No Yes Yes