Yes, you’re going to want to get SATA drives that are the same size or bigger than your SAS drives. The mini-sas will break out into 4x sas connectors but you don’t have to swap 4 at a time; disconnect one SAS drive from the SAS breakout cable and then connect one replacement SATA drive to the SATA backplane (either the one on your motherboard or to a SATA card if you don’t have enough mobo ports). Do a zfs scrub. Once it’s finished with no errors, repeat all three steps. Once all drives are off the SAS card and your final scrub is done you can remove the SAS card entirely.


Yes, if you’re going to run TrueNAS (or another solution based on ZFS) you should really get rid of the PERC and get an LSI SAS card in IT mode so that the system can see the raw disks.
When you start your SATA swap, either use the onboard SATA ports (if there are enough) or get a SATA card (more ports, probably slightly better performance than sharing the onboard controller) and start the process I described before.