OWC includes the driver for the Accelsior card as shipped and calls it out visually in the packaging, but one could forget to install it either at initial install or when installing a fresh system. For example, if you’re testing out Mavericks as a fresh system install, install the driver for the Accelsior PCIe SSD. Ditto for any fresh system install.
If the Accelsior PCIe SSD is used in the OWC Mercury Helios case, then a driver is not needed. As per OWC:
Note: Driver ensures proper power-down of Accelsior during sleep, restart, and shutdown actions that may otherwise not occur in the Mac Pro with PCIe connected drive volumes. This driver does not affect or interact with other drivers, software applications, hardware devices, etc.
This driver is not required for use of Accelsior in Thunderbolt to PCIe Expansion chassis (such as OWC Helios). No driver is required for use of Accelsior for Windows or Linux operating systems.
* The OWC driver for the Accelsior PCIe SSD addresses a behavior (bug) introduced in OS X in which power is cut off prematurely to PCIe cards. This premature power cut-off bug was introduced in an OS X release a good time after I first tested and reported on the Accelsior.
The driver for the Accelsior PCIe SSD inserts a sub-second delay, giving the PCIe card time to finish its business (pending writes). Under Microsoft Windows on the same machine, no driver is needed (because the OS does not have this bug).
The power cut issue would apply to any PCIe card that needs time to do housekeeping before the power is cut, e.g. a hardware RAID card or other PCIe SSD.
Upgrading to the E2
Separately and not related to the above, MPG recommends upgrading to the Accelsior E2 version to gain a new chipset and dual eSATA ports. This is a module swap onto a replacement (bare) card.