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29.4 Rest for the Hard Disk
In Linux, the hard disk can be put to sleep entirely if it is not needed or it can be run in
a more economic or quieter mode. On modern laptops, you do not need to switch off
the hard disks manually, because they automatically enter an economic operating mode
whenever they are not needed. However, if you want to maximize power savings, test
some of the following methods. Most of the functions can be controlled with powersaved
and the YaST power management module, which is discussed in further detail in
tion 29.6, "The YaST Power Management Module"
The hdparm application can be used to modify various hard disk settings. The option
-y instantly switches the hard disk to the standby mode. -Y puts it to sleep. hdparm
-S x causes the hard disk to be spun down after a certain period of inactivity. Replace
x as follows: 0 disables this mechanism, causing the hard disk to run continuously.
Values from 1 to 240 are multiplied by 5 seconds. Values from 241 to 251 correspond
to 1 to 11 times 30 minutes.
Internal power saving options of the hard disk can be controlled with the option -B.
Select a value from 0 to 255 for maximum saving to maximum throughput. The result
depends on the hard disk used and is difficult to assess. To make a hard disk quieter,
use the option -M. Select a value from 128 to 254 for quiet to fast.
Often, it is not so easy to put the hard disk to sleep. In Linux, numerous processes write
to the hard disk, waking it up repeatedly. Therefore, it is important to understand how
Linux handles data that needs to be written to the hard disk. First, all data is buffered
in the RAM. This buffer is monitored by the kernel update daemon (kupdated). When
the data reaches a certain age limit or when the buffer is filled to a certain degree, the
buffer content is flushed to the hard disk. The buffer size is dynamic and depends on
the size of the memory and the system load. By default, kupdated is set to short intervals
to achieve maximum data integrity. It checks the buffer every 5 seconds and notifies
the bdflush daemon when data is older than 30 seconds or the buffer reaches a fill level
of 30%. The bdflush daemon then writes the data to the hard disk. It also writes inde-
pendently from kupdated if, for instance, the buffer is full.
WARNING: Impairment of the Data Integrity
Changes to the kernel update daemon settings endanger the data integrity.
532
Installation and Administration
(page 541).
Sec-
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Troubleshooting
