[Lustre-discuss] xserve raid

[Andreas Dilger]

On Oct 17, 2007  15:35 -0400, Brock Palen wrote:
> We are doing some testing,
> 
> For a OST with a xserve raid connected to linux,  is it better to not  
> have a partition table
> 
> mkfs.lustre /dev/sda
> 
> or to have a partition?
> fdisk /dev/sda
> mkfs.lustre /dev/sda1

For RAID 5/6 devices we recommend NOT having a partition table.  The reason
is that the partition table offsets the data partitions by a small amount
(512 bytes usually) and this causes writes to span multiple RAID chunks and
unnecessary read-modify-write activity.

For best performance, pick a RAID chunk size that divides evenly into
1MB (e.g. 4 or 8 data disks + parity).  The ldiskfs mballoc code works
to align the allocation with the RAID chunk size for best performance.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.