HP StorageWorks Scalable File Share - Manual (Page 66)

For workloads that require a lot of disk head movement relative to the amount of data moved,
SAS disk drives provide a significant performance benefit.
Random writes present additional complications beyond those involved in random reads. These
additional complications are related to Lustre locking, and the type of RAID used. Small random
writes to a RAID6 volume requires a read-modify-write sequence to update a portion of a RAID
stripe and compute a new parity block. RAID1, which does not require a read-modify-write
sequence, even for small writes, can improve performance. This is why RAID1 is recommended
for the MDS.
66 HP SFS G3 Performance