vinum in 4.x poor performer?

[Mark A. Garcia]

Olivier Nicole wrote:

>>All servers run RAID5 .. only one other is using vinum, the other 3 are 
>>using hardware RAID controllers ...
>>    
>>
>
>
>Come on, of course a software solution will be slower than an hardware
>solution. What would you expect? :))
>
>(Given it is same disk type/speed/controler...)
>
>  
>
Usually this is the case, but it's also very dependent on the hardware 
raid controller.  There are situations where a software raid (vinum in 
this case) can outperform some hardward controlers under specific 
circumstances, i.e. sequential reads w/very large stripe size.  An 
example is an image server where the average image might be 3MB.  A 
stripe size of 434kB would cause ~7 transfers of data.  A case for a 
larger stripe size of 5MB would greatly improve performance.  There 
would be an 2MB diff in the avg file size that doesn't have any useable 
data.  Only 1 transfer of data would occur.  Vinum optimizes the data 
transfered to the exact 3MB of the file, whereas some hardware controls 
would transfer the whole 5MB stripe, adding some bandwidth latency and 
transfer time.  Again, it's a matter of specific cases, and assuming 
'performance' based on differing conduits for data transfer can just 
skirt the real issue, if there is any.

Cheers,
-.mag