Re: RAID 1 versus RAID 5

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Date: Mon, 29 Nov 2004 13:33:15 -0800

Kevin I would point out that this configuration precludes any disk space
being added to your system. This is why the standard has been mirror [raid1]
the OS and stripe [raid 5/0+1/10] the data.

Here is the reason why. It is common to need to add disk space to the data
partition/drive. Most raid controllers don't allow dynamic upgrades in the
raid array. So to add more disk space with your present configuration you
have to wipe the existing array and recreate the raid5 array with the
additional disk so you have more space. This usually means you have to
repartition the way you want, reinstall the OS and backup software and
restore from a backup. A long painful process.

Lets say you have a raid controller that can add the disk to the array
dynamicly. Great. Now you have system, apps and data partitions. How are
you going to add the "unallocated space" to the data partition? You only
have two options. The best being buy a server version of Partition Magic and
use it to add the space to data. Or create a volume set between the data
partition and the unallocated space [very bad choice since I have seen chkdsk
/f destroy a volume set].

Now if you had mirrored the OS and stripped the data [in your case apps and
data] it is a simple matter of backup apps and data, reinit the array with
the added disk, use disk manager to partition as you desire and format the
partitions. Then restore from backup. I have done this in 4 hours on a Sat.
[depending on how long it took to init the array and restore data].

Lets say you wanted to make the OS drive space larger. You can't mirror to
a larger drive. But you can break the mirror, use ghost to ghost from small
driver to larger and then with another larger drive in the system mirror the
two. Again a fairly straight forward operation which you can not do if you
have all three partitions on a single raid5 array. This is a two hour or
less operation.

Just something to think about.

"Kevin Weilbacher" wrote:

> Fred, I know way back when it was recommended not to use raid-5 for your
> system partition. But I don't believe that is applicable any longer. I know
> I use hardware Raid-5 for all my SBS servers without any problems. I take my
> 3 or 4 drives, set them up in Raid-5, and partition them into 3 sections:
> system, apps, data.

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