In reading through TechRepublic discussion
forums, I stumbled across a very recent discussion where member mccoygreg asked
questions about software
RAID capacity, and some other members chimed in with their comments
regarding software RAID. As a result of this discussion, I thought I’d put
together a quick RAID primer and offer some of my own opinions about the issue
of hardware vs. software RAID solutions.

If you’re interested in some pretty in-depth information about
how RAID works,
take a look at the article I originally wrote for TechProGuild. While that
article went in-depth about a bunch of different RAID levels, I’m going to
focus on only RAID levels 0 (striping), 1 (mirroring), and 5 (striping with
parity) in this article.

First, I want to address the storage dilemma posed by
mccoygreg, who is setting up a lab server so he can play to his heart’s
content. He indicated that he purchased a new 80-GB drive that he wanted to use
in conjunction with his existing 6-GB and 8-GB drives. Unfortunately, while he
can create a RAID-5 array, because of the way RAID-5 works, he will lose 74 GB
capacity on his shiny new drive. Why? RAID-5 requires drives of equal capacity.
For situations in which the selected drives differ in size, RAID-5 defaults to
the least common denominator. In this case, the smallest drive is 6 GB in size,
so the RAID-5 configuration will use only 6 GB from the other two drives as well,
and the remaining space is ignored.

If mccoygreg wants to use the total capacity of 80 GB, he
would need to purchase two more 80-GB drives, since RAID-5 requires three
drives in order to operate. Mccoygreg’s other alternative is to forgo RAID-5
and use RAID-0 instead, which provides the ability to use the maximum capacity
of each individual disk. In this case, a RAID-0 array would result in a total
of 92 GB of capacity. I would strongly recommend against this approach,
however. In a RAID-0 configuration, the loss of a single disk results in the loss
of all data on the array. By using RAID-0 on three disks, mccoygreg would
triple his chances for complete data loss.

RAID-1-mirroring requires two drives of equal size, so the 6-GB
and 8-GB drives might be good, but the member would still lose 2 GB from the 8-GB
drive, since RAID-1 also uses the smallest disk size in cases where the drives
sizes differ.

I’ve said a couple of times that mismatched drive sizes
default to the smallest of the individual drives. Note, however, that this
doesn’t always work. Some RAID controllers really require identical drives.

Finally, let’s address the issue of software vs. hardware
RAID. As one member pointed out, software RAID is like playing with fire. If
you have a server hiccup, you could have some data loss issues. However, even
though RAID hardware has come down in price, it’s still not always feasible for
organizations to incur the additional expense, or perhaps you’re using older
servers that don’t have RAID hardware. In these cases, if you want to further
protect your data, use software RAID. It’s definitely better than having no
RAID at all! And, Windows 2000 and Windows Server 2003’s handling of these
kinds of scenarios is really pretty good, though not as reliable as a hardware
solution.

These days, all new servers in my environment use either
RAID-1 or RAID-5, and, with the exception of a couple of older servers that
will soon be virtualized, all servers use hardware RAID controllers, rather
than relying on the Windows RAID feature.

TechRepublic’s free Storage NetNote newsletter is designed to help you manage the critical data in your enterprise. Automatically sign up today!