[nmglug] Hardware RAID5 vs Software RAID5

[Nick Frost]

Tim Emerick wrote:

> Is the advantage of using a hardware raid over a software raid as the 
> author notes all that great? 

This is a difficult issue, as you will receive opinions of both sides 
(hardware RAID vs. Software).

A couple of thoughts.

- true hardware RAID offloads the RAID overhead to the RAID card, thus 
less overhead on the computer. Software RAID is cheaper, more flexible, 
but uses CPU cycles whereas true hardware RAID does not (use CPU).

- in my opinion, for computers that are not heavily utilized (multi-user 
servers), the impact of software RAID in terms of load on the computer 
is negligible. I am typing this on a Linux workstation that is doing 
software RAID-1 (2 disc mirror) and rarely do I notice disc I/O issues 
due to the RAID setup.

However, if you are planning on re-utilizing a Pentium 400 Mhz as a 
RAID-5 NAS, you may get better performance with a 3ware or LSI IDE (or 
SATA) raid card.  However, if you look at this article;

http://www.chemistry.wustl.edu/~gelb/castle_raid.html

the software RAID performance, once tuned is nearly equivalent for an 
EXT3 file system when compared to hardware RAID with a 3ware card.  If 
you can get an LSI megaraid i4 from ebay for < $200.00 you could run 
your own hardware raid vs. software RAID benchmarks by setting up 
hardware RAID, running bonnie++ and iozone, and then configuring 4 
drives as JBOD and doing software RAID.

- while I have not experienced a hardware failure on a hardware RAID 
card, I think the chances of data recovery are better with Software 
RAID, though I am sure some will disagree with me. Actually that's not 
entirely true, I built a workstation based on an Abit KG7A-RAID some 
years go, and did hardware RAID on the Highpoint controller (which isn't 
true hardware RAID, it's really firmware/software RAID, but nevermind). 
A disc failed, I put in a new one, went into the Highpoint BIOS, rebuilt 
the mirror, rebooted the machine, and the Webmaster kept working 
(resumed where he left off).

- RAID is not a backup. In either instance, emphasis should be placed on 
creating an automated backup solution.  With Linux this is easy, if you 
have a two disc RAID-1 configuration, simply add a third disc and Rsync 
what you want to back up to that third disc, or Rsync to a file server 
or other device on  your LAN, or an external USB drive for that matter. 
  For home networks, the Linksys NSLU2 with a USB drive is an affordable 
network storage device that can be used for backups with any client OS. 
  For small business, something like and Infrant ReadyNAS (RAID 5, 
$1,200.00) is a decent choice for a backup server, if you don't want to 
roll your own.

- if you have an IDE RAID setup (firmware RAID) and drive zero (channel 
0) develops corruption (bad sectors) this may propagate the corrupted 
data to the 2nd disc on channel 1; again backups are important 
regardless of what RAID technology or scenario is implemented.

Hope that helps.

-Nick
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Nicholas S. Frost
nickf at nickorama.com