Lustre 1.6 Operations Manual

10.1.4 Performance Considerations
Currently, we are improving the Linux software RAID code to preserve large I/O
which the disk subsystems can do very efficiently. With existing RAID code
software, RAID performs equally with all stride sizes, but we expect that fairly large
stride sizes will prove advantageous when these fixes are implemented.
For better performance, we recommend that you use a couple of smaller OSTs,
instead of fewer, large-size OSTs. Following this recommendation will provide you
with more IOPS, by having independent RAID sets instead of a single one.
10.1.5 Formatting
When formatting a filesystem on a RAID device, it is beneficial to specify additional
parameters at the time of formatting. This ensures that the filesystem is optimized
for the underlying disk geometry. Use the --mkfsoptions parameter to specify
these options in the Lustre configuration.
For RAID5, RAID6, RAID1+0 storage, specifying the -E stride=
option improves the layout of the filesystem metadata ensuring that no single disk
contains all of the allocation bitmaps. The parameter is in units of 4096-
byte blocks and represents the amount of contiguous data written to a single disk
before moving to the next disk. This is applicable to both MDS and OST filesystems.
Note – It is better to have the MDS on RAID1+0 than on RAID5 or RAID6.
For more information on how to override the defaults while formatting MDS or OST
filesystems, see Options to Format MDT and OST Filesystems.
10-4 Lustre 1.6 Operations Manual • September 2008