Clear the page cache

sync && echo 1 > /proc/sys/vm/drop_caches

Clear the dentries and inodes

sync && echo 2 > /proc/sys/vm/drop_caches

Clear the pagecache, dentries and inodes

sync && echo 3 > /proc/sys/vm/drop_caches 

Samsung Rapid Mode (caching)

The Load Cycle Count (LCC) is the number of times the head has been moved to the parked position. That typically happens when the drive is idle for some time, shutdown or it is powered down to save power. Drives are specified for a LCC of around 500.000

A high load cycle count, parking the heads, might damage a drive. On Linux there is a tool for Western Digital dirves to set the interval time or disable the load cycling. idle3-tools. run as

idle3

For Seagate drives we did not find a tool yet

Known ATA S.M.A.R.T. attributes (see 193 for the LCC)
Mac os X harddisk high load cyclecounts
The load cycle count of Western Digital Caviar Green hard drives

hdapm: Hard Drive Advanced Power Management (this is a program)
hdapm usage guide
hdparm can be used to lower the number of times the drive spins down thus avoiding wear
This can be done by setting APM to Always On: hdparm -B 254
Not all manufactures follow the specification. Experimentation might be needed

smartctl is in the smartmontools package along with smartd

For reading harddisk temperatures use smartctl

for i in {a..d}; do smartctl -x /dev/sd$i | grep Temperature_Celsius | tr -s " " | cut -d ' ' -f 8; done

fstrim Discard (or “trim”) unused blocks on a mounted filesystem which are not in use by the filesystem. This is useful for solid-state drives (SSDs) and thinly-provisioned storage.

fstrim / -v 

Fill unused blocks with zero's (0x00). An other value can also be choosen with the

• -f option. An octet value between 0 and 255
• -n for dry-run
• -v for verbose

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