[mythtv-users] New Frontend, Any gotchas with Compact Flash storage

[Paul Bender]

Mike Isely wrote:
> On Mon, 3 Mar 2008, Paul Bender wrote:
> 
>> Matthew Asplund wrote:
>>>
>>> Would things be better if there was a small disk in RAM for stuff like 
>>> /tmp and /var? Then you could pretty much have / be a read-only file 
>>> system, with all writable stuff copied in the ramdisk and then lost on 
>>> reboot.
> 
> This is in fact exactly what I did when I set up my two diskless 
> front-ends which share the same NFS root file system on the back end.  
> I'm a Debian user and the "stock" Debian setup has a tmpfs partition 
> pre-configured for a few things like this already (ifupdown state).  It 
> was just a matter of identifying other similar areas and sym-linking 
> appropriately.  I also wrote a tiny little startup script that uses 
> rsync to copy a template mirror hierarchy (very very small - to set up 
> the in-RAM structure and for a few tiny bits of initialized read/write 
> data) into the ram disk so that the symbolic links automatically point 
> to the correct valid subtrees.
> 
> One really slick added bonus is that even after all that, the system is 
> still 99% maintainable as a normal stock Debian installation (so far).
> 
> 
>> Essentially, that is what live distributions as well as MiniMyth do, 
>> albeit in a somewhat different fashion. They create a RAM disk that they 
>> overlay on the entire root file system using a stackable file system 
>> such as unionfs. This makes the entire file system appear to be 
>> read-write. However, all changes are lost after reboot.
> 
> I thought about this approach (i.e. use unionfs).  I also thought about 
> just shrinking the entire root fs down small enough that it could just 
> live entirely in RAM.  But in the end (1) I didn't like the idea of 
> having to pull an out-of-tree driver (unionfs) into the kernel, and (2) 
> I would need probably at least 2GB of RAM on the FE to make the 
> full-time root ramdisk viable.

MiniMyth runs the entire image from RAM. However, since the image is 
compressed, it is read-only. Therefore, unionfs is used to make it 
read-write.

MiniMyth supports SDTV resolution displays using 512MB of RAM and 
supports HDTV resolution displays using 1024MB of RAM, so 2GB of RAM 
would be somewhat overkill.