1 file system, 2 drives?

Michael Powell nightrecon at hotmail.com
Tue Jul 27 14:39:43 UTC 2010

krad wrote:
>> If you have hardware controller with RAID capabilities, using native RAID
>> is better, otherwise look towards gvinum or maybe ccd; see also:
>>  http://www.freebsd.org/doc/en/books/handbook/raid.html
> I dont agree that hardware raid is necessarily better. It really depends
> on what the system is doing. If for example it is purely acting as a filer
> I would always use software raid. The main reason for this is that you
> benefit from the faster CPU, and more intelligent raid software (zfs). You
> are also not tied to a particular hardware platform which makes future
> upgrades easier.

In the bad old days (early) days hardware RAID was clearly better. This is 
not as true today as CPUs have scaled. The 3GHz plus quad cores of today 
have cycles to spare and can actually make software RAID faster in many 
situations. The questionable area would be RAID 5 and 6. The XOR processing 
done in the hardware controller is expensive, and hardware RAID is still 
probably a better way to go here.

Other features such as hot swap, hot spare, scrubbing, and 
maintenance/monitoring utilities will be easier to find in the hardware RAID 
> If however the system is doing lots of other things and you dont want the
> overhead of a software raid solution, it makes  sense to offload it to a
> hardware solution

Very expensive controllers are expensive because the processor on the card 
has more horsepower, which typically shows up in IO/s numbers as well as 
throughput as multi-thread queue depths rise.

It is a shame to need to spend serious money on these cards just to get the 
inherent raw processor power even though you may turn off the RAID 
functionality and instead use ZFS and raidz. There is still a performance 
advantage to be seen because of the higher processing power available from a 
controller processor that has bigger umphh.


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