[Lustre-discuss] OST RAID setup - best practices

[Bill Wichser]

Reading through the Lustre documentation, it is still unclear to me 
about how to best set up the underlying RAID arrays.

Three OSSes connect to 3 disk drawers with 15 drives.  These are 
directly connected SATA drawers with no connections between the OSSes.

My initial feeling was to set these up as 4+2 (RAID6), two per drawer, 
as the documentation states that more OSTs are better than fewer.  This 
would allow 256K blocks with the stride of 1M.  So far, so good.

The argument has been made that more spindles provide better 
performance.  So 8+2.  The 128K blocks still allow 1M stride across the 
8 spindles.

Because we have 15 drives though, a 12+2 (with always 1 hot spare) and a 
  possible block size of 256K, stride 3M, this might be a much better 
option.

I'm kinda stuck in this 1M block though that Lustre seems to want to 
throw around.  Is there any reason that the underlying disk structure 
needs to match this exactly to get the best performance?  Or am I 
believing in some urban legend here?  Does the Raid card, with it's 
cache just hide this all from Lustre anyway?

Any insight would be appreciated.  Thanks.

Bill