No, this is not about a bug killer.
This is about Redundant Array of Inexpensive Disks (RAID).
Don't get fooled by this fancy title. The RAID concept is not as complicated
to understand as the name implies.
Basically RAID technology stores your data on more than one drive to make sure nothing
gets lost and to allow recovery of data from failed disk drives without
shutting the system down. In computer jargon, we are talking
about data integrity and reliability.
Intended for Servers
RAID normally applies to a server system where vast and important amounts of data
are stored and it is constantly being changed. For most companies,
if their server goes down, the entire company sits around staring
at each other until all the King's men put the server back together again.
Like everything associated with computers, just to make it complicated, there is more
than one method of RAID technology. RAID types vary from
RAID 0 to RAID 10. Some of the levels have only slight variations.
For the sake of clarity, only RAID levels 0,1 and 5 are going to
be covered here. RAID can not
be accomplished with a single drive. Depending on the RAID level, a minimum of two or three drives is required.
What is it?
RAID 0 uses a method of writing to the disks called striping. Let's
assume you have a server with three drives of 500MB, 1 GB and 2 GB.
Normally a server would treat each of these drives individually. By
incorporating striping, the system would see all of the drives as
only one drive for a total of 1.5GB. Why only 1.5GB? Because the maximum used on each drive can't exceed the size of the smallest drive. So it is best to have drives of the same size when using striping.
When the system writes data to the disk, the RAID 0 striping kicks in and automatically
distributes the data across all three drives. Part of a file (chunks
of data) will be written to the first drive, the next part to the
second drive, the next part to the third drive and then it starts
all over again until the entire contents of the file have been written.
What this does is increase the speed of the reading/writing process.
If you have two drives on your server, it increases the speed by about
25%. If you have three drives, it increases the speed about 33%. When
you consider that the main task a server is performing is reading
and writing data, any increase in speed is highly welcome.
Besides increasing speed, the other benefit is that the drives can be of different sizes.
Because RAID 0 only writes the data once, it does not achieve data
redundancy. If one of the drives fails, the entire system has to be restored because
all files are split or striped across all drives. Because there
is no data redundancy, there is no loss of disk space.
Adding a RAID controller and more drives.
What is it?
RAID 1 uses a technology called mirroring or disk shadowing. RAID
1 requires a minimum of two drives that are exactly the same size.
Every time a write is executed the same data is written to both drives,
i.e. a mirror image. Well, almost a mirror image. The data is not reversed in the same way as when you look in the mirror.
So what you achieve with RAID 1 is data redundancy. If one of the drives fails,
the system can continue to run by just writing to one drive. If you
have hot swappable drives, you could pull out the bad drive, plug
in a new one and the system is back to its normal state. How efficient
and easy it is to execute all of this depends onthe RAID controller and/or software that is being used.
There is basically no increase or decrease in the time it takes to write or read data.
The disadvantage of RAID 1 is that you lose half of your disk capacity. If
you have two 4GB drives, you don't have a total of 8 GB of space,
but only 4 GB. So you are losing half of the capacity of disk space
that you paid for. But on the other hand disk drives are fairly inexpensive
today. What has to be considered is what is the cost of downtime
if a drive fails on your server? The downtime cost is probably much more than the cost of the additional drive.
RAID 1 can be accomplished by simply adding another drive and perhaps you may need a new controller that supports RAID. It is possible to use a RAID
software controller, but we don't recommend it. Windows servers and some versions
of the Linux/UNIX/AIX operating systems provide the mirroring software. Configuration
and installation is fairly simple. So, for a few hundred dollars you can quickly have RAID 1 up and working.
What is it?
RAID 5 accomplishes both techniques of RAID 0 and RAID 1.
There are other benefits of RAID 5 but lets leave that discussion
to the techies. You'll just have to take my word for it.
RAID 5 requires a minimum of three drives and it is recommended that all drives on the system be of the same
size. The more drives you have on the server, the better RAID 5 will
perform. We usually recommend having five drives where one is used as a spare. This will allow for up to two drives to fail and the system can keep running.
RAID 5 is the version most often recommended. Because the price of disk drives have
drastically dropped, the cost of implementing RAID 5 is now within most companies budgets.
There is a decrease in write speed due to calculations that have to be made before data is written to the drives. If you want to increase read/write speed and have the benefits of RAID 5, you need to implement RAID 10.
The loss of disk space is basically 100 divided by the number of disk drives. With
3 drives, there is a 33% loss of disk space. With 5 drives, there is a 20% loss of disk space.
RAID 5 is more expensive to implement. You will need additional drives and a RAID
controller. The cost of implementing RAID 5 could be in the range of $1000 to $5000 depending on the total number
of drives, type of drives and controller required.
Is it worth it?
If you ...
- value your data
- can't afford any downtime
- consider the cost of recovery when you have a drive failure
Yes it is!
Until companies have a drive failure, most companies don't consider or view this technology
as being valuable. Don't let yourself fall in that trap. Give the
benefits of RAID some thought. To help prove the benefits, you might
want to shutdown your server for an hour and discover how unproductive
your organization can become. Of course this is a very short time
compared to an actual drive replacement and data recovery that could take up to two or more days.