2 April
2002
"To
be or not to be, that is the question"...oops, wrong
question. While we may not be facing the same challenges Hamlet
faced, choosing whether to climb the mountain called RAID
can still be vexing. Once only a luxury for the server crowd,
"Lite" versions of IDE RAID are now available to
the masses.
For
many years, I used tape drives to backup my PC. However, as
time went by, I would have to keep buying larger tape drives
to keep up with the sheer volume of data on my hard drive.
Eventually, my diligent backing up slacked off as more and
more tapes were required to complete a single backup. Occasionally
I would make a Ghost image of my drive, but I did it so infrequently,
it was hardly a reliable backup (and DVD-RW/+RW is still too
expensive). In the end, I gave up data security altogether
by having no backups. As I was planning my next upgrade, I
read an article in MaximumPC magazine that recommended buying
a motherboard with a built-in hardware RAID controller. Their
position was that even if you didn't use the RAID capabilities,
you could still split your IDE drives on to separate RAID
channels. If you had four IDE devices, each would have its
own IDE channel, thus minimizing traffic on each channel.
So I paid the extra and purchased the Abit KR7A-RAID motherboard.
Overview
In a basic
sense, RAID is simply hard drives working together. RAID
stands for Redundant Array of Inexpensive (or sometimes "Independent")
Disks. It is a method of combining several hard drives into
one logical unit. The levels of RAID are as follows:
|
RAID
0 |
RAID
1 |
RAID
0+1
|
RAID
5 |
RAID
0+5 |
| Description |
Data
striping
(no data protection)
|
Disk
mirroring
|
RAID
0 and RAID 1 combined
|
Data
striping with distributed parity
|
RAID
0 and RAID 5 combined
|
| Minimum
# of Drives |
2
|
2
|
4
|
3
|
6
|
| Benefit |
Highest
performance
|
Data
protection through redundancy
|
Highest
performance with data protection
|
Best
balance
of cost/
performance/
data protection
|
Provides
increased fault tolerance
|
The
lite IDE controllers usually provide RAID 0, RAID 1 and RAID
0+1. Two of the newer onboard hardware Ultra133 IDE RAID solutions
are the Promise
20271 and the HPT374
controller. Peripheral cards may also offer Level 5 and
0+5 RAID. Finally, there are also third-party and OS software-based
RAID solutions.
Since
this article is concerned with inexpensive data protection,
it will only examine RAID Level 1. In order to satisfy my
data protection needs, I had to decide between a weekly backup
to a second drive or configure the two drives for RAID 1.
What follows is a discussion of some of the Pros and Cons
of implementing RAID Level 1.
Pros
Realtime
data security - This is the main reason for Level 1 RAID;
it provides data protection by duplicating all data from a
primary drive on a secondary drive. The second drive is an
exact copy of the first drive. Data is written to both drives
at the same time. In the event one drive fails, the other
drive is an exact duplicate.
No
additional partition letters - In Windows Explorer, you
do not "see" the second drive's partition letters.
Improved
Read Times - During a read, only one drive is typically
accessed, but the controller can use both drives to perform
two independent accesses. Thus, mirroring improves positioning
performance. However, once the data is found, it will be read
off one drive; therefore, mirroring will not really improve
sequential performance.
Cons
Realtime
data security - RAID Level 1's greatest asset is also
it's greatest liability. In the event that you screw up something
like your Operating System (been there, done that), it's likely
that the backup is also screwed up.
Additional
wear on second drive - If only weekly backups are performed,
the second drive would see only occassional use, but RAID
1 would have the second drive used just as often as the main
drive.
Slower
write times - During a write, both hard disks are used
and performance may be slightly worse than it would be for
a single drive.
Less
storage space - For example, with two 60GB drives, the
total usable storage space is 60GB and not 120GB.
Final
Thoughts
I
tend to tinker and tweak my Operating System (Windows XP)
a lot. A couple of weeks ago I nearly corrupted my system
with a bad driver install. Life would have been much easier
if I had a backup handy. With RAID Level 1, I would have corrupted
the second drive as well as the main drive. For me, a weekly
backup is more appropriate. However, if data security is paramount,
then RAID Level 1 may be exactly what you need.
Additional
Resources -The following are good resources for additional
information about RAID and provided background for some of
the items above
Adaptec
Storage
Review
VIA
Arena
