Choosing the Right Disk Technology in a High Availability Environment DRAFT Version 2.0, August 1996

DRAFT -- Revision 2.0
August 22, 1996Page 23
+ lower cost for moderate to large configurations
+ easy on-line replacement of failed disk mechanisms in RAID 1, 0/1, and 5
+ capability to immediately assign a hot standby spindle to take over for a failed
spindle
+ highest storage connectivity since each array uses only 1 or 2 SCSI target
addresses
+ flexibility of configuration
select among a choice of RAID levels 0, 0/1, 5
multiple RAID levels in one array concurrently
+ potential for high performance in a small I/O size, read-intensive environment
+ dual storage processors (controllers) and power supplies reduce the number
of SPOFs
+ automatic storage processor failover with HP-UX Revision 10.0
+ global hot spare disk mechanisms
- little control over the placement of data for application performance tuning
- variable overall performance depending on RAID level, I/O size, and read or
write
- the Storage Processors may potentially be a bottleneck
- performance degradation will occur for small reads if a disk spindle in RAID
level 5 mode has failed since the array controller must read from the other
spindles to recalculate the missing data
- although HADAs have redundant power supplies, there is only one power cord
that means that the power source is an SPOF
- no boot support in a multi-initiator (shared bus) environment
- UPSs required for powerfail support
- RS-232 link is required for configuration
There is an additional disadvantage worth mentioning that applies only to the FLDAs
and SCSI DAs:
- adding disk mechanisms requires a reload of the data except in Independent
Mode
Disk Arrays with AutoRAID
HP offers a disk array with a patented technology named AutoRAID, called the HP Disk
Array with AutoRAID, henceforth called AutoRAID array for brevity. Two configurations
are available, as product numbers A3515A (Deskside) and A3516A/[Z] (Rackmount).
These arrays have the following features:
combines RAID 0/1 and RAID 5 in the same array
automatically migrates data between RAID modes according to access
patterns