[mythtv-users] sluggish system, potential HD failure, and how best to get back up and runnin

[Simon Hobson]

Hika van den Hoven <hikavdh at gmail.com> wrote:

> Note the difference between ramfs
> and tmpfs. ramfs assigns space at need and tmpfs assigns an in kernel
> predefined size. A size you can change with kernel options.

As I read things, that's not correct.
ramfs doesn't limit the size - so you can keep writing until memory is all used up and OOM killer will crash the system. tmpfs has a fixed upper size which you can set at mount time.
I'm pretty certain that neither allocates the memory until it is actually used. I have a system (sort of semi-embedded and running from a CF card) where I've put several volatile filesystems on tmpfs - and until I realised the presence of the size option, I had the tmpfs volumes adding up to twice the available ram (and no swap on the system).

https://wiki.debian.org/ramfs

https://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt
> tmpfs puts everything into the kernel internal caches and grows and
> shrinks to accommodate the files it contains ...

http://www.thegeekstuff.com/2008/11/overview-of-ramfs-and-tmpfs-on-linux/