[K12OSN] Linux "Software RAID"

[Les Mikesell]

Rob Owens wrote:
> 
>> raid5: automatically using best checksumming function: pIII_sse
>>    pIII_sse  :  2604.000 MB/sec
>> raid5: using function: pIII_sse (2604.000 MB/sec)

> I don't see any of that info on my systems with software RAID 1.

Raid1 doesn't do any calculations - it just tells the hardware to write 
twice and reads from whichever copy is faster.  Any performance hit 
comes from CPU involvement during writes (not much unless you are on old 
IDE or USB connections) or overloading the PCI bus.

 > What
> do those values mean?  Are they read speads?  Write speeds?

That's the math to compute the parity that needs to be written along 
with the data.  And if you have a failed drive in the set it will do a 
similar computation to reconstruct the data in degraded mode (where 
raid1 just reads the other copy at full speed).

-- 
   Les Mikesell
    lesmikesell at gmail.com