HP StorageWorks Scalable File Share System Installation and Upgrade Guide Version 2.2

SFS20 storage — overview and planning 5–21
5.3.3 ADG and RAID5 redundancy
This section compares the basic hardware RAID capabilities of a single SFS20 array and describes the
issues that need to be taken into account when you are determining which type of RAID redundancy to use.
NOTE: To maximize data integrity and simplify disk replacement, HP recommends that SFS20 arrays in
new customer installations are configured with ADG (RAID 6) redundancy.
NOTE: You also have the option of configuring your storage so that data is mirrored between SFS20
arrays; this provides another level of data protection.
NOTE: If 500GB disks are used, only ADG redundancy is supported.
The following considerations can be used to determine whether you want to configure ADG (also called
RAID6) or RAID5 redundancy on your SFS20 arrays:
• Availability
When ADG redundancy is used, the data parity is written to two separate disks. Arrays that are
configured with ADG redundancy are thus immune to two concurrent disk failures, whereas RAID5
redundancy can accommodate single disk failures while maintaining LUN integrity. Figure 5-6 and
Figure 5-7 show how RAID5 and ADG redundancy functionality write data to the backing disks. For
information on the rebuild times for active RAID5 LUNs, refer to Appendix D of the HP StorageWorks
Scalable File Share System User Guide. The rebuild time is the window of exposure for a RAID5 LUN.
Figure 5-6 Data parity—RAID5
Figure 5-7 Data parity—ADG (RAID6)