RAID block map

Klennet RAID Viewer builds a block ordering map for a given set of disks, start sector, block size, and various other parameters.

Map elements and controls

The block map screen has these elements, in top to bottom order:

  • Disk reordering buttons (left and right arrow).
  • Disk name, not editable.
  • Include/exclude disk checkbox.
    Uncheck this if you want to exclude any of the disks from the display. The background analysis process collects the data for excluded disks, so if you change your mind and want the excluded disk back, there is no time penatly associated with it.
  • The block map itself, automatically generated and not editable.
  • Mirror threshold selector.
    How close must two drives match to be considered identical (members of the same mirror set). Only whole sector matches are counted, and blank (all zeros) sectors are not included.
  • Number of rows setting.
    The number of rows controls how many blocks form the repeating RAID pattern. In a RAID where there are no mirrors, no missing disks, and no extra disks, the number of rows equals the number of disks. The following basic rules apply:
    1. If there are missing disks, the number of rows equals the number of available disks plus the number of missing disks;
    2. if there are mirrored disk pairs, one pair of mirrors counts for one row;
    3. if there is an extra disk (hot spare), the number of rows should be decreased by one.
  • Parity mode selector.
    Configures how many parity blocks to display, per disk. Possible settings are
    • None for non-parity arrays like RAID0 or RAID10;
    • One for single parity arrays: RAID4, RAID5, and RAID50;
    • Two for dual parity arrays: RAID6 and RAID60.


Block map of a RAID6.

Block map of a RAID6

Block map of a RAID10 with an extra drive.

Block map of a RAID10 with an extra drive

Interpreting the block map

There are the following cues on the block map.

  • Colored columns, including the extra row at the very bottom of the column, mark sets of identical or near-identical drives. Typically, the set consists of two disks, but in some cases there may be three.
  • Gray shading indicates parity. If two-parity mode is selected for a RAID6, darker block typically corresponds to Reed-Solomon (second) parity. However, the part of the analysis identifying which parity is XOR and which is Reed-Solomon is not always reliable.
  • Sequence arrows show in which order blocks follow each other. If the arrow starts or ends on the parity block or on the block of the excluded drive, this arrow is not shown. Therefore, blocks can exist which are not included in the sequence, that is, do not have an arrow passing through them. Typically, if you have such unconnected blocks, something is wrong with the parameters.

I recommend one disk of every mirror pair is excluded from display by unchecking the corresponding checkbox, and then move them all to the right side in order to reduce visual clutter.

Disks unrelated to the array typically produce a straight vertical line of arrows, as shown on the RAID10 example above.