HP ProLiant Server Drive compatibility

There was a huge change between G7 and Gen8 when it comes to 2.5" disk caddies - they simply won't fix into each other. To be fair the Gen8/9 caddies offer a lot of additional functionality that the G7 version couldn't but it was rather a testing time for a lot of organisations who had become used to generation-to-generation interoperability.

So to confirm, they're not forward or backwardly compatible.

The bare disks are compatible. Assuming you speaking of regular 2.5" SAS disks.

However, drives for G7 servers are cheap. Buy some from eBay and you won't have to deal with the caddy swap or any other unnecessary changes.