Monday, May 9, 2011

RAID 1 array is able to improve average access time

In theory at least, RAID1 can improve average access time (but not random access time) during the read.
This defies widely-held belief that RAID array cannot reduce access time.

RAID1 has two disks with two identical copies of data. If read operations are organized as follows:

  • first member disk serves the read operations to the first half of the disk,
  • the second disk handles the second part of the data,
then the average length which a read head should travel to locate a sector is reduced by the factor of two.
Based on the above it is not possible to improve rotational latency. In any case, performance increases since less head travel is needed.
In RAID 1 there is no improvement on writes since both member disks should be synchronized.