[mythtv-users] Software RAID (was: Where are those new 1TB drives?)

Brian Wood beww at beww.org
Thu Mar 8 18:36:09 UTC 2007

On Mar 8, 2007, at 8:49 AM, match at ece.utah.edu wrote:

> On 7 Mar 2007 at 22:08, Jim - MythTV wrote:
>> How well does software raid work? is it worth going with? I was  
>> hoping to setup a FreeNAS
>> server, I have an old external 10 drive bay cdrom tower that I was  
>> planning on putting in3 icy
>> docs (2x 5 drive and 1 x 3 drive version (13 drives total) (if I  
>> can find a reasonable place in canada
>> that sells em) Probably go with a few
>> 5 750;s to start and fill the others as i get the cash :)
>> oh couse would have to get a couple 5 port sata cards.
> Along time ago... In a galaxy far, far away... before the days of  
> MythTV...
> before SATA... In the days when 20 gig hard drives ruled the day...

Of course I go back to when a 20 meg hard drive was HUGE, and rivaled  
a 747 in spool-up noise. A controller board (ISA buss of course) cost  
more than a modern 500 gig drive.

Then, before that, there were the pre-Winchester Control Data "Bird"  
series (Hawk etc.). You would let a removable platter sit for 24  
hours to stabilize to room temperature before you would dare spin it up.

Then there were drums...

But in the days you are talking about, say around mid-2000, we did  
some comparisons of RAID-5 arrays using Linux software RAID and the  
high-priced hardware RAID controllers being sold.

The software solution compared very favorably. The overhead could be  
measured but had no real-world impact on performance, these were  
single and dual 600-700 Mhz. machines.

The biggest problem we ran into with the H/W RAID was that if a  
controller failed you sometimes had to get the EXACT same controller  
in order to get your data back, and some of the early controllers  
were replaced with "improved" units very quickly. The controllers  
were also very touchy as to precisely what drives they would work  
with. Some of these problems are alleviated today though.

OTOH a software RAID disk created back then could be read today with  
no trouble. No vendor lock-in or obsolescence problems, fewer slots  
taken up, less power consumed and less up-front cost.

With today's CPUs the overhead is negligible. I'd go with software RAID.

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