The following table shows the possible status values for CacheDrives listed in the MCM Devices page.

Device is online.  This is the normal expected status for a healthy system.
Device is offline.  It may be powered off or unable to reach the Internet.
Firmware download in progress.  The firmware image is about 100 MB in size, so generally the CacheDrive should not stay in this state for very long.
Firmware update in progress.  The device should not stay in this state for more than a few minutes.  Do not power off the CacheDrive until the update is complete.
A reboot has been scheduled to complete the firmware update process.
Device is rebooting.
Device is syncing with the cloud.  Normally, this status only appears when a large amount of data needs to be synced (initial sync of a new device, bringing online a device that has been offline for an extended period, etc.)
The device could not access its cache disk.  On VMs, this can happen if the boot disk is not removed.  This status may also appear briefly during initial setup, but if it persists, contact support.  
This status may appear briefly during initial setup.  If it persists, contact support.
Device is processing a file that is taking an unusually long period of time.  This may be due to file size, slow network speed, or cloud connectivity.  If this status persists and is unexpected with the file shown, contact support.
General error message.  Contact support.

For more information on the status of a CacheDrive, please see the following article: