Macintosh bootable volumes are supported on the internal 2-port PCI card (part number TSATA) but are not supported on any of the other SATA cards at this time.
This condition occurs when the System Preferences Energy Saver Put the hard disk(s) to sleep when possible checkbox is checked (on), or the Disk Sleep Timer is enabled; the Tempo-X SATA card using firmware version 1.2 does not support disk sleep.
To correct this issue, update the Tempo-X card's firmware to version 2.0 or later. Download and run the installer to add disk sleep support.
Another manufacturer's previously-installed SATA driver may be accessing a Sonnet SATA card in error causing a drive access slowdown. For example, we have seen Fusion D400QR5 performance drop from 200MB/s to under 50MB/s in such circumstances. The solution is to remove the other manufacturer's SATA driver.