Jochen Keil writes:
> Hi.
> 
> Daniel Carosone wrote:
> > To resolve this, if you can, add a fifth disk and choose your stripe
> > size and filesystem block size carefully so the filesystem blocks
> > exactly map to a full stripe write.  Otherwise, you'd be much better
> > off with stripe+mirror over the four disks.
> 
> My setup is quite similar to Mihai's. The differences are that it has 
> one channel for every disk and i'm using 200gb disks.
> I'm satisfied with my performance (~11mb/s on random write) but after 
> your email i was wondering if there could be some optimisation.
> At the moment i'm doing a benchmark on my 4 disk R5 setup and later i 
> will do so on a 3 disk R5. What i'm wondering about is your comment 
> about matching stripe size and file system block size.
> Default FS block size is 16kb for partitions above 1024MB. I'm using 
> this R5 Layout:
>   START layout
>             # sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level
>             32 1 1 5
> I learned that 32 blocks equal to 16KB. As far as i can see my block 
> size matches my stripe size so this is the optimum. 

No.  In this case, with "4 data disks", a full stripe will hold 
4*32=128 blocks (64K) of data.  (That "32" is per-component.)

So a block size of 64K will probably perform the best with this 
configuration.

Later...

Greg Oster