Default on battery APM level causes SSD runing very slow

[Yanling]

Installed Ubuntu 16.04 on a Dell 7559 laptop with Crucial MX300 750GB SSD. When power is unplugged, file read/write speed is about 30MB/s consistently. When power is plugged, file read/write speed is about 400~500MB/s consistently.

Used hdparm to check SSD status and found APM level is 128 on battery and 254 on power.

Edited /etc/hdparm.conf to set apm_battery=254 and after reboot file read/write speed back to normal 400~500MB/s.

Not sure if this is a feature or bug but on battery APM level 128 had caused SSD running ridiculously slow (~30MB/s).

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. It seems that your bug report is not filed about a specific source package though, rather it is just filed against Ubuntu in general. It is important that bug reports be filed about source packages so that people interested in the package can find the bugs about it. You can find some hints about determining what package your bug might be about at https://wiki.ubuntu.com/Bugs/FindRightPackage. You might also ask for help in the #ubuntu-bugs irc channel on Freenode.

To change the source package that this bug is filed about visit https://bugs.launchpad.net/ubuntu/+bug/1650074/+editstatus and add the package name in the text box next to the word Package.

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[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Alberto Salvia Novella (es20490446e)]

Full explanation at:
https://askubuntu.com/questions/844459/ubuntu-ssd-was-fast-is-now-extremely-slow

[Alberto Salvia Novella (es20490446e)]

Work around:
https://wiki.archlinux.org/index.php/hdparm#Persistent_configuration_using_udev_rule

[Marco Zaccari (marcozaccari)]

In my Ubuntu 18.10 neither udev rule or hdparms.conf works.
Instead I needed to edit /etc/default/tlp changing DISK_APM_LEVEL_ON_BAT value.