SSD, hangs at shutdown Synchronizing SCSI cache

Netrunner Netrunner Desktop 17.01
1

I’ve installed on an existing SSD partition. It doesn’t seem the installer is customizing for SSDs.

Cannot gracefully shutdown or reboot. Why? After removing “quiet” from the Grub entry I find the system consistently hangs at

sd 0:0:0:0 [sda] Synchronizing SCSI cache

Until this point all services exit properly.

I installed hdparm and executed

sudo hdparm -W0 -k1 /dev/sda

and

sudo hdparm -F /dev/sda

. This allows for a happy shutdown. I did have a STARTUP hang on the swap partition /dev/sda3 a couple times, not consistent so maybe unrelated.

I’d like to use SSD write cache buffer, so… Why is my system hanging? What does “sd 0:0:0:0” mean, systemd and system disk?

I noticed the fstrim.service wasn’t configured by the installer. I have setup the service and timer.

Update: I forgot to mention, I put the write cache flag back and no more hang yet… Why?

sudo hdparm -W1 -k1 /dev/sda
2

With writeback cache enabled the data that is intend to be written to the ssd is instead written to a cache. The long “hanging” at shutdown could indicate it writing huge stuff from that cache back to ssd.
Basically it should then after a couple of minutes if writing finished turn off normally.