about 1-2 min to shutdown or reboot
Kernel 4.8.1 SSD drive
Here is start of messages
ata 2.00: exception emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
ata 2.00: cmd a0/00:00:00:08:00/00:00:00:00:00:00/a0 tag 27 pio 16327 in
Get event notification 4a 01 00 00 10 00 00 00 08 00res 40/00:00:00:00/00:00:00:00/00 Emask 0x4 (timeout)
ata 2.00: status ( DRDY ) ata 2.00: revalidation failed (errno=-5)
Machine is stock Dell i5 optiplex 9020 about 1-1/2 yrs old -- case and fan are clean inside, connections are tight, disk (short) test shows OK,
Windows shuts down normally
I think problem started about a month ago