How to DEFER disk write entirely, for protect hard disk?

lwjandmy · 07-31-2015, 01:44 PM

I have 64bit Ubuntu 14.04 on my laptop, 4GB RAM,160GB hard disk.

I usually typping code, lying on the bed, so vibration is often, I know this is harm to hard disk.
So I want to defer disk write, delay few minutes then flush whole data to disk.

I have set root's mount option with 'noatime':

Code:

   $ mount
   /dev/sda1 on / type ext4 (rw,noatime,errors=remount-ro)

And set vm_dirty options:

Code:

   $ sysctl -a | grep dirty
   vm.dirty_background_bytes = 0
   vm.dirty_background_ratio = 5
   vm.dirty_bytes = 0
   vm.dirty_expire_centisecs = 60000
   vm.dirty_ratio = 10
   vm.dirty_writeback_centisecs = 500

But I found that isn't work, this is my test:

Code:

   # flush data to disk
   sync   ( command finished immediately, cause I just enter system, no other buzy process working)

   # make a test file
   touch test ( the HDD led flash, means disk WORK on this command !  Data should be cached ?! )

   # add some  text
   echo 'a' >> test ( led flash again ! )

   # much more  text
   echo 'a' >> test
   echo 'a' >> test
   echo 'a' >> test ( this three test, only first and second , HDD led flashs ; the third, led no change)

I fell puzzled at this test.
I have set defer write, but when I add 'a' to file, the disk work directly, without caching.

What should I do further more, for succeed defer disk write ??

michaelk · 07-31-2015, 05:30 PM

Welcome to LinuxQuestions.

Unless your tossing the laptop around in bed my first thought is that there is nothing to worry about. How much protection depends on latpop and hard drive manufactures. There is inherently some form of dampening in either the hard drive itself and / or mounting provisions. Depending on age and manufacture some drives have built in vibration / shock detection so if critical values are exceeded the heads are automatically retracted.

lwjandmy · 07-31-2015, 11:13 PM

Quote:

Originally Posted by michaelk

Welcome to LinuxQuestions.

Unless your tossing the laptop around in bed my first thought is that there is nothing to worry about. How much protection depends on latpop and hard drive manufactures. There is inherently some form of dampening in either the hard drive itself and / or mounting provisions. Depending on age and manufacture some drives have built in vibration / shock detection so if critical values are exceeded the heads are automatically retracted.

Thanks for reply.

Could you please tell me:
"I have set defer write, but when I add 'a' to file, the disk work directly, without caching." Why the cache didn't work?

Thanks again.

michaelk · 08-01-2015, 06:32 AM

I've never played with those parameters but dirty_writeback_centisecs = 500 which is a 0.5 seconds which could be the reason your not getting the desired results. Another parameter that might work for you is increasing ext4 commit.