Using a DRU that is larger than the PPU in Transparent RAID

For flexibility sake and to allow easy future disk size expansion, Transparent RAID allows users to use a DRU that is physically larger than the PPU.

This is odd given that a DRU must always be smaller or equal to the smallest PPU in order to achieve parity protection.

When a DRU that is larger than the smallest PPU is used in Transparent RAID, users are required to create a partition that is smaller than the smallest PPU disk and leave the remainder of the space un-partitioned and unused.
This is allowed so that the full disk can be used later on when the user upgrades the PPU disk to a larger disk.

So, let’s say you have the following config:
- 2TB DRU
- 2TB DRU
- 3TB DRU
- 2TB PPU

The 3TB DRU is larger than the PPU and would technically not be supported.
However, because Transparent RAID is flexible, you can use such disk, but you must create a partition less than 2TB on the disk. Note how it is stated that the partition must be less (and NOT lesser or equal). It must strictly be less.
A good rule of thumb would be to make the partition about 1GB less than the smallest PPU.

Finally, the partition should be created at the start of the disk and not the end of the disk.

Failing to follow this requirement will leave the larger DRU vulnerable as its space above the smallest PPU size will not be recoverable if that drive was to fail.

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