What are the limitations when resizing a SoftRAID Volume?

Note: SoftRAID does not support adding disks to expand an existing RAID 5 volume. For example, you cannot start with a 3-disk RAID 5 volume and add a fourth disk to extend it. The only exception is mirror volumes, which allow for additional disk additions.

Expanding by replacing disks with larger ones

You can expand a RAID volume by replacing existing disks with larger ones. Here is how it works:

Example: You have a RAID 5 volume with four 12TB drives (36TB usable space). You replace each 12TB drive one at a time with 18TB drives. After all drives are replaced, you still have a 36TB volume. SoftRAID then allows you to expand the volume to take advantage of the new drive sizes, giving you up to 54TB of usable storage.

HFS+ resize limitations

Only the last created volume on a RAID array can be resized.

Note: When you resize an HFS+ volume, the allocation block size remains fixed from when the volume was originally formatted. This means there is a limit to how much larger a volume can grow – once the fixed block size can no longer address the expanded capacity, further resizing is not possible without reformatting. The exact limit depends on the original volume size and the block size assigned at format time, so results may vary.

APFS has no such limitation

With APFS, there are no allocation block constraints – volumes can be resized indefinitely as capacity increases.