Re: software RAID vs hardware RAID


Subject: Re: software RAID vs hardware RAID
From: Joshua J.Kugler (isd@as.uaf.edu)
Date: Fri Mar 14 2003 - 12:17:00 AKST


On Friday 14 March 2003 11:42, Damien Hull wrote:
> 1. It seems more difficult to repair or fix a bad drive

It shouldn't be, as the software drivers should detect the new drive and take
appropriate action. There might be a rebuild command that has to be issued
from the command line.

> 2. Including /root in the RAID array requires a work around

True, but if *I* did a setup like this, I would probably have a system drive
for /, applications, etc, and then put data (mail, database, etc) on the RAID
partition (even if I used symlinks).

> 3. Performance will be better with hardware RAID

Yes and no. With mirroring and striping, you are simply writing (or reading)
data to/from two drives. There is no real overhead involved. With RAID 5,
you are computing checksum bits, so writing will be slower with software
RAID, but reading should be just as fast.

YOU SHOULD ALSO KEEP IN MIND: IDE raid cards from Promise. Adaptec, and
HighPoint are not true hardware RAID! They use system drivers to do the RAID
1/0/1+0 operations. In fact, I've heard that there has been admission (by
said companies) that the Linux software drivers are actually better than
their proprietary drivers. I believe the only true hardware IDE RAID card
out there is from 3Ware.

> The RAID array must be able to keep the system running even if one of
> the drives fails. This means I need to have /root mounted on the array.

Umm...I don't think that's correct. Are you sure?

> Also, I'm using Debian so any info on getting software RAID working
> under Debian would be a big help.

There is a RAID utilities package, that should make things easier.

> So far I like the money saving aspect of software RAID but it looks like
> I might save my self a lot of time and a headache or two using a
> hardware solution.

Maybe...reading the man pages for the RAID utilities should tell you all you
need to know. I'm sure there is a RAID HOW-TO. Also, the RAID drivers for
Promise, Adaptec, etc, do funny things to the drive, and write housekeeping
data in funny places. You might just be better off with Linux RAID if you
are just doing mirroring.

Hope that helps.

j----- k-----

-- 
Joshua Kugler, Information Services Director
Associated Students of the University of Alaska Fairbanks
isd@asuaf.org, 907-474-7601

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