/tmp, /var/log, /var/tmp as /dev/md - why?

[Ronald Klop]

On Tue, 01 Jul 2014 12:46:19 +0200, Anton Shterenlikht <mexas at bris.ac.uk>  
wrote:

>> From r.c.ladan at gmail.com Tue Jul  1 11:37:35 2014
>>
>> 2014-07-01 11:25 GMT+02:00 Anton Shterenlikht <mexas at bris.ac.uk>:
>>
>>> Why is it a good idea to mount /tmp and some var dirs on memory disks:
>>>
>>> root at raspberry-pi:/usr/ports # df -m
>>> Filesystem     1M-blocks Used Avail Capacity  Mounted on
>>> /dev/mmcsd0s2a     14694  777 12742     6%    /
>>> devfs                  0    0     0   100%    /dev
>>> /dev/mmcsd0s1         16    3    13    20%    /boot/msdos
>>> /dev/md0              28    4    22    16%    /tmp
>>> /dev/md1              14    0    12     0%    /var/log
>>> /dev/md2               4    0     4     0%    /var/tmp
>>> root at raspberry-pi:/usr/ports #
>>>
>>> Is this about speed or power, or maybe space?
>>>
>>> Mostly write tear because you're using an SD card, and it improves  
>>> speed
>> too.
>
> "write tear"?
> Is this a joke, or some technical term?
> I cannot find what it means.

If you search for "write tear ssd" you get a lot of hits. It means that a  
lot of people like to reduce the number of writes to flash disks.


> I get these messages on the console (well, on hdmi port...):
>
> pid ... (svnlite), uid 0 inumber 13 on /tmp: filesystem full
>
> If I unmount /tmp from md and leave it on sd card,
> then I don't see these anymore. What does this mean?

That the default setup is not suitable for your use case, because you  
write more to /tmp than the person who made the installation.
And that you can change the /tmp mount as you like.


Regards,
Ronald.