[systemd-devel] How to spin down a disc with systemd?

[poma]

On 30.04.2014 13:02, Lennart Poettering wrote:
> On Wed, 30.04.14 01:02, Marcin Kocur (marcin2006 at gmail.com) wrote:
> 
>> Hello all,
>>
>> I wrote a service /etc/systemd/system/disable-2nd-hdd.service. I
>> have 2 HDD's where one of them doesn't need to work all the time. So
>> I thought it'd be cool to shut it down after 30 minutes of
>> inactivity (the disc isn't mounted when system starts):
>> /usr/bin/hdparm -S 241 /dev/sdb
>>
>> Then I wrote a service:
>>
>> [Unit]
>> Description=Disable sdb
>> Requires=local-fs.target
>> After=local-fs.target
> 
> These two lines are implied and hence can be removed.
> 
>>
>> [Service]
>> Type=oneshot
>> ExecStart=/usr/bin/hdparm -S 241 /dev/sdb
>>
>> [Install]
>> WantedBy=multi-user.target
>>
>> Which seems to work:
>>
>> [root at linux mk]# systemctl status disable-2nd-hdd.service
>> ● disable-2nd-hdd.service - Disable sdb
>> Loaded: loaded (/etc/systemd/system/disable-2nd-hdd.service; enabled)
>> Active: inactive (dead) since pon 2014-04-28 10:00:53 CEST; 21min ago
>> Main PID: 248 (code=exited, status=0/SUCCESS)
>>
>> kwi 28 10:00:53 linux hdparm[248]: /dev/sdb:
>> kwi 28 10:00:53 linux hdparm[248]: setting standby to 241 (30 minutes)
>>
>> But it doesn't work, like it had never happened, the disc is not spun down.
>>
>> When I change the command to /usr/bin/hdparm -y /dev/sdb (spin down
>> disc immediately), the disc is spun down while booting but is starts
>> again right away.
>>
>> When I manually start this service after system has already booted,
>> it works as expected.
> 
> Note that devices are probed asynchronously, and a device not needed at
> boot is not waited for. THis means that your service might run before
> the harddisk showed up in the kernel, or possibly that your hdparm
> command is invoked before the initializating/probing/identifying of the
> hdd or its filesystems is compelted, thus possibly negating the effect
> of your command.
> 
> YOu probably want to invoke your commandn with RUN from a udev rule so
> that it is run when the hw is found.
> 
> Lennart
> 

e.g.
/etc/udev/rules.d/99-diskungfu.rules
ACTION=="add", SUBSYSTEM=="block", DRIVERS=="ahci",
RUN+="/usr/bin/diskungfu"

disk spindown - sdparm
https://lists.fedoraproject.org/pipermail/users/2013-April/434786.html

systemd/cron functionality
https://wiki.archlinux.org/index.php/Systemd/cron_functionality


poma