gstripe performance oddity

[Maxim Sobolev]

Joel Jacobson wrote:
> i tried sending this to freebsd-geom but got no response, so i'll try a 
> higher traffic superset list...
> 
> i have a bit of a weird issue, which i suspect is a configuration 
> problem, and was looking for a little advice.  i have an LSI JBOD box 
> with a bunch of SAS drives that i would like to gstripe together.  each 
> drive individually seems to be able to do about 80 MB/sec streaming 
> write, and doing parallel dd's gives me the 160 MB/sec i would expect.  
> if i gstripe them together with a 256k stripe width, i only see 80 
> MB/sec, though.
> 
> if, however, i newfs/mount it as ufs and then dd myself a big file, that 
> gets me about 120-130 MB/sec.
> 
> why does mounting matter?

You will see dd write speed increase on stripe only if you are using 
block size (bs=XX) larger than stripe size, so that you should try dd 
bs=512k or something and see if it helps.

-Maxim