To minimize power usage during sleep, power is removed from PCIe cards. Because of this power-saving specification, a USB 3 PCIe card is unable to maintain USB port power during sleep. In macOS, this result in a storage device disconnect upon wake from sleep. The storage device will automatically remount, but the system reports a disconnect message. Because macOS flushes all caches before sleeping, this disconnect should never result in any loss of data.
These cards are compatible with only Thunderbolt 2 or 3 PCIe expansion chassis; they are not compatible with Thunderbolt 1 PCIe expansion chassis (unless they have been upgraded to Thunderbolt 2).
