Total cost of ownership and the cost of downtime are more
difficult to quantify, but here are some items to consider when
comparing software- and hardware-based RAID solutions.
User productivity. Faster RAID performance means
faster system response time and increased user productivity. As
demonstrated with both empirical and benchmarked data,
hardware-based RAID frequently outperforms software-based RAID,
but the real question is whether the difference is noticeable and
therefore cost-justifiable. There are several instances where
hardware-based RAID is likely to produce noticeable results. These
include CPU-bound applications, workstation applications such as
NASTRAN and AutoCAD where card-based caching has a significant
impact, and in frequently accessed RAID 1 arrays where RAID 0/1's
parallel disk accessing and load balancing effects offer clear
advantages over simple mirroring.
There are two situations where hardware-based RAID solutions
have a direct and noticeable effect on user productivity no matter
what the application. The first situation is the length of time
your application runs in RAID 5 degraded performance due to a
failed drive. Hardware-based RAID solutions that automatically
detect the failed drive, replace it with a spare, and rebuild the
array, eliminate the need for manual intervention and reduce the
time your application is running in degraded mode. The second
situation is if your boot drive fails. With hardware-based RAID,
you can RAID-protect your boot drive and keep your system up and
operational, eliminating the need to replace the failed drive or
restore files from tape in order to bring the system back into
operation.
Management costs. Frequent studies have concluded
that the cost of managing storage far outweighs the initial
acquisition costs. Although difficult to quantify for your
particular environment, the cost savings due to reduced management
and training time by being able to view all storage-related errors
color-coded by severity for all NT and Netware servers from
a single remote console, to schedule pro-active maintenance
activities, and to poll server, network and non-RAID cards may
justify the 15% premium of a hardware-based solution.
Reconfiguration costs. These days, few
installations remain static for very long. The ability to expand,
reuse, and reconfigure your storage can be an important
requirement, not only to save on your hardware and software costs,
but also training and management costs. Regardless of whether you
use software- or hardware-based RAID, selecting a storage card
that can expand to multiple device channels allows you to expand
storage capacity as your needs grow, and to optimize channel
performance by placing slower or more frequently accessed devices
on separate channels, all without having to use up another PCI bus
slot. For mixed operating system environments, employing
hardware-based RAID typically means that a simple inexpensive
device driver is all that's needed to reconfigure your storage
from a Windows NT to a Novell Netware environment - no new
training costs, no new cards, and same management console.
