[CentOS] Harware vs Kernel RAID (was Re: External SATA enclosures: SiI3124 and CentOS 5?)

[Michael A. Peters]

Gordon Messmer wrote:
> On 06/01/2009 07:52 PM, Michael A. Peters wrote:
>> I've read a lot of different reports that suggest at this point in time,
>> kernel software raid is in most cases better than controller raid.
> 
> There are certainly a lot of people who feel that way.  It depends on 
> what your priorities are.  Hardware RAID has the advantage of offloading 
> some calculations from the CPU, and has a write cache which can decrease 
> memory use.  However, both of those are relatively expensive, and 
> there's no clear evidence that your money is better put into the RAID 
> card than into faster CPU and more memory.  Another important 
> consideration is that hardware RAID will (must!) have a battery backup 
> so that any scheduled writes can be completed later in the case of power 
> loss.  If you decide to use software RAID, I would strongly advise you 
> to use a UPS, and to make sure your system monitors it and shuts down in 
> the event of power loss.

Yes - my home systems are all on UPS with automated shutdown after 5 
minutes of no power. Display is on there too, so that in event of power 
outage while I'm using, I can save all my work.

I guess from the discussion that hardware raid is definitely still the 
way to go for servers, where the guy at the colo can simply swap out a 
dead drive if need be w/o any serious downtime etc.

What I'm personally interested in doing is building an amanda server for 
my home network, backing up /home and /etc from my 3 other computers, 
but virtual tapes (disk images) instead of real tapes, once blueray 
media becomes cheap enough to burn the virtual tapes as a secondary 
backup, but I primarily want the virtual tapes stored on a redundant 
raid so that recovering will be easier (no need to go from blue ray 
unless the raid failed)

I'm guessing for that software raid is probably good enough because the 
unit will be idle most of the time and cpu cycles won't be a needed 
commodity. In fact, I may even want something that sleeps and wakes on 
lan activity so that it doesn't waste as much power when it's just 
sitting there.