Disk drives will eventually fail, no matter how high an MTBF
rating. To protect your system from unscheduled downtime, RAID
technology should be implemented in every server. Software- and
hardware-based RAID are both viable technologies that will
continue to thrive for the foreseeable future, offering clear
tradeoffs in cost versus functionality. (See What
is RAID for more information).
Hardware-based RAID solutions offer availability and
serviceability advantages over software-based RAID, such as the
ability to detect more bit errors and to correct some of them;
RAID-protected bootable arrays; automatic failed drive detection,
spare replacement and array rebuild; pooled or dedicated spares;
alarms color-coded by severity; and remote monitoring and
management of multiple RAID installations and multiple operating
systems from a single console.
The installation procedures for software- and hardware-based
RAID solutions are simply different, - neither is better or more
time consuming than the other. Good RAID solutions feature
intuitive, user-friendly Windows-like graphical user interfaces,
with simple shortcuts to get first-time RAID users up and running
quickly as well as more sophisticated features for advanced users
to optimally tune their RAID configuration.
In CPU-bound applications, the advantages of hardware-based
RAID are clear - reduced CPU interrupts and reduced main PCI bus
traffic result in better overall system performance. In I/O-bound
applications, while the differences may not be as great,
hardware-based RAID is advantageous in several situations, such as
decreased time your RAID 5 array runs in degraded mode, the
ability to stripe boot arrays, and using RAID 0/1 instead of RAID
1 for improved performance.
Clearly, the up front costs of software-based RAID are hard to
beat - they're free. The incremental cost of an entry-level
hardware-based RAID solution is less than you might think -
typically about 15% - because software-based RAID solutions still
require a SCSI host card. When total cost of ownership is
considered, the hidden costs of software-based RAID in terms of
user productivity, management costs, and reconfiguration costs
often result in a higher overall total cost of ownership than
hardware-based RAID solutions.
