Second Member of Mirror or Stripe Set Larger than First

This article was previously published under Q101629

When Windows NT creates a mirror set, stripe set, or stripe set with parity, the sizes of the disk partitions are approximately equal. Windows NT reserves some additional space for administrative data. However, when the disk geometry of the disk drives involved is not identical, the Disk Administrator rounds the size of the second member UP to the nearest cylinder boundary. Depending upon the controller used and BIOS settings this may make the size of the secondary member partition larger than the first partition. The extra space in the second partition is not used.

Some SCSI controller BIOS's translate drives larger than 1GB to make 1 cylinders worth of data be equal to up to 8MB - in that case the rounding UP can make the secondary partition 8MB larger.

If the drive is not used for booting - translation is not necessary, and can be disabled to eliminate the 8MB rounding but the drive must be re- formatted after doing so.

Note that Windows NT Workstation does not support mirroring or stripe sets with parity.