08-31-2011
I'm familiar with SDD in a SAN environment. Not a laptop/PC.
If there are a lot of large "hot" files, specifically ones that are read all the time, then disk with an SDD buffer will improve read performance. One 15000 rpm SAS drive can post a max of ~200 iops. SDD can do 3000 iops. But this only works when the SDD already has the data you want to read.
If your apps write then immediately read the data SDD has just written, then SDD helps there as well. But then disks come with a large buffer cache anyway, SDD or not.
Bottom line: SDD helps when there is "smart use", i.e., maybe like MRU retention kinds of algorithms that databases use in shared memory. As a "dumb" buffer SDD helps, but I don't know the help it provides justifies the cost difference.
SAN software actively moves files into tier 1 (like SDD) based on observed historical demand. This REALLY helps performance.
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LEARN ABOUT MOJAVE
systemd-suspend-then-hibernate.service
SYSTEMD-SUSPEND.SERVICE(8) systemd-suspend.service SYSTEMD-SUSPEND.SERVICE(8)
NAME
systemd-suspend.service, systemd-hibernate.service, systemd-hybrid-sleep.service, systemd-suspend-then-hibernate.service, systemd-sleep -
System sleep state logic
SYNOPSIS
systemd-suspend.service
systemd-hibernate.service
systemd-hybrid-sleep.service
systemd-suspend-then-hibernate.service
/lib/systemd/system-sleep
DESCRIPTION
systemd-suspend.service is a system service that is pulled in by suspend.target and is responsible for the actual system suspend.
Similarly, systemd-hibernate.service is pulled in by hibernate.target to execute the actual hibernation. Finally,
systemd-hybrid-sleep.service is pulled in by hybrid-sleep.target to execute hybrid hibernation with system suspend and pulled in by
suspend-then-hibernate.target to execute system suspend with a timeout that will activate hibernate later.
Immediately before entering system suspend and/or hibernation systemd-suspend.service (and the other mentioned units, respectively) will
run all executables in /lib/systemd/system-sleep/ and pass two arguments to them. The first argument will be "pre", the second either
"suspend", "hibernate", "hybrid-sleep", or "suspend-then-hibernate" depending on the chosen action. Immediately after leaving system
suspend and/or hibernation the same executables are run, but the first argument is now "post". All executables in this directory are
executed in parallel, and execution of the action is not continued until all executables have finished.
Note that scripts or binaries dropped in /lib/systemd/system-sleep/ are intended for local use only and should be considered hacks. If
applications want to react to system suspend/hibernation and resume, they should rather use the Inhibitor interface[1].
Note that systemd-suspend.service, systemd-hibernate.service, and systemd-hybrid-sleep.service systemd-suspend-then-hibernate.service
should never be executed directly. Instead, trigger system sleep states with a command such as "systemctl suspend" or similar.
Internally, this service will echo a string like "mem" into /sys/power/state, to trigger the actual system suspend. What exactly is written
where can be configured in the "[Sleep]" section of /etc/systemd/sleep.conf or a sleep.conf.d file. See systemd-sleep.conf(5).
OPTIONS
systemd-sleep understands the following commands:
-h, --help
Print a short help text and exit.
--version
Print a short version string and exit.
suspend, hibernate, hybrid-sleep, suspend-then-hibernate
Suspend, hibernate, suspend then hibernate, or put the system to hybrid sleep.
SEE ALSO
systemd-sleep.conf(5), systemd(1), systemctl(1), systemd.special(7), systemd-halt.service(8)
NOTES
1. Inhibitor interface
https://www.freedesktop.org/wiki/Software/systemd/inhibit
systemd 237 SYSTEMD-SUSPEND.SERVICE(8)