The devb-umass driver does not support sync so you must specify the sync=ignore option to the mount command, or to the driver directly when starting it. E.g.
# mount -tqnx6 -o sync=ignore /dev/hd10t177 /fs/flash
NOTE: In newer SDP versions, "sync=ignore" is not documented (but may still work). The supported/documented option is "sync=none".
NOTE:
This entry has been validated against the SDP version listed above. Use
caution when considering this advice for any other SDP version. For
supported releases, please reach out to QNX Technical Support if you have any questions/concerns.