First Sector Value for Software RAID

In software RAID, the first track of a component disk contains the master boot record and is not part of the RAID. A track usually contains 63 sectors (except for some IBM disks with 32 sectors). Data is stored starting at sector 63 (or 32 for IBM disks).

If a disk is wholly allocated to a RAID, the First Sector value for reconstruction is this value. This is also true for mixed-use disks where the first disk extent (an extent is very similar to a partition) is allocated to the RAID. See Figure 19.4.

Calculating this value is difficult for disks with other extents preceding the RAID extent. To determine the starting sector of the RAID disk area, you must use a disk utility such as dmdiag, available from Microsoft®. In Figure 19.4, the First Sector value for Disk 3 (assuming this is not an IBM disk) is 63. The First Sector value for Disk 2 is 63 plus the size of volume E (in sectors) and possibly a small gap of a few (0 to 7) unused sectors between the first and second partition.

Figure 19.4: A software RAID 0 (drive D) configured on mixed-use disks.