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tmpfs is not a ramdisk (was: delimiters with more than one character? ...)



rhkramer@gmail.com (12020-07-17):
> I'm not the op, but, in what sense do you say that?

tmpfs is FILESYSTEM backed in memory. A ramdisk is a kind of DISK, i.e.
a block device, backed in memory and in which you can store a filesystem
if you want.

There are significant differences, like the fact that a file removed
from a tmpfs will really free the memory and make it available for the
system, while a file removed from a filesystem stored on ramdisk will
just have its data marked as available for the same filesystem.
(Nowadays, a ramdisk could implement the trim features, but that's
piling hacks on top of hacks.)

There are also performance differences, because filesystems are designed
to ensure consistency over catastrophic interruptions, which is
completely useless if the data itself does not survive catastrophic
interruptions.

> I use tmpfs filesystems for files that either I want fast access to (ram speed) 
> or want to make sure they disappear on reboot / power loss.
> 
> I have tried to do a little reading since I saw this, I see some references 
> that say it is stored on RAM, some others that say it is stored in virtual 
> memory and could be on swap.

I am pretty sure it can be on swap. If you want to be sure, just test:
create a tmpfs larger than your physical memory, and fill it with a big
file.

> Among other things, should I be worried that it won't disappear on power loss 
> / reboot?

Depends on what kind of disappear you want. If all you want is not to
have to worry about cleaning up, then you are good with tmpfs.

If you are worried that sensitive data may end up on disk, then encrypt
your swap with an ephemeral key.

Regards,

-- 
  Nicolas George

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