The problems with "hardware" RAID are the proprietary disk formats and the need to buy multiple RAID cards in case one fails, as you may need to have the same v

The problems with "hardware" RAID are the proprietary disk formats and the need to buy multiple RAID cards in case one fails, as you may need to have the same vendor/version for it to be a straight swap and still keep all your data. There can also be issues with drivers, especially if the "hardware" RAID is partly implemented by the driver. I've had issues in the past with needing to put hardward RAID drivers into the initramfs of Linux boxes just so that they can boot. With software RAID, you can just plug the disks into other servers without those kinds of problems.