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 can’t start with a 3-disk RAID 5 volume and add a fourth disk to extend it. The only exception is with mirror volumes, which allow for disk additions.

However, you can expand a RAID volume by replacing existing disks with larger ones. Here’s how it works:

Example: Suppose you have a RAID 5 volume with four 12TB drives (totaling 36TB usable space). If you want to increase capacity, you could replace each 12TB drive one by one with 18TB drives. After all drives are replaced, you would still have a 36TB volume. SoftRAID then allows you to expand this to utilize the new drive sizes, giving you up to 54TB of usable storage.

Limitations to Expansion:

Only the last created volume on a RAID array can be resized.
If you’re using HFS+ as the file system, you can’t expand a volume if it exceeds an allocation block boundary.

HFS+ allows you to resize past the next level, but no further. A 16TB volume can be resized to 64TB, but no further. A 32TB volume can be resized to 128TB.

With APFS, however, there are no such allocation block constraints, allowing for indefinite volume resizing as capacity increases.