You can create a RAID1 spanning an SSDs and HDDs with Linux software raid. This makes sense to profit from the advantages of both technologies as much as possible. Use the
--write-mostly for mdadm for HDDs to specify that they should be avoided for reads.
From the mdadm man page:
--write-mostlysubsequent devices listed in a
--addcommand will be flagged as ‘write-mostly’. This is valid for RAID1 only and means that the ‘md’ driver will avoid reading from these devices if at all possible. This can be useful if mirroring over a slow link.