[PC-BSD Dev] Wild idea to speed up boot process

Claudio L. claudio at hpgcc3.org
Mon Aug 19 16:28:10 PDT 2013


On 08/19/2013 15:43, Warner Losh wrote:
> Two issues here:
>
> (1) The buffer cache will make reading off media as fast as reading from RAM (since you need to load the RAM, and the delta in compression is likely tiny since configuration data from /etc is tiny). I'm not sure it would help much in the boot time.
What makes me think (and hope) it will, is the random read speed vs 
sequential read speed. A normal HD can do 120 MB/s sequential, but about 
4 MB/s random, and that's where the improvement will come from.
I'm not only thinking about /etc, but almost everything needed for 
booting, including executable files and everything else.
Or perhaps I'm looking at it wrong, and what we really need to do is 
find a way to persist the disk cache across reboots (?).

> (2) NanoBSD has a mechanism to cope with all the issues that you are talking about here. You might want to look at what it does. It doesn't bother with unionfs, preferring instead to load the "known good" configuration from persistent media into RAM and running from there (although there's a minor issue with /etc/master.passwd when users change their passwords).
I didn't know that. I'll definitely look at their code before attempting 
anything.
Thanks for the hint!

Claudio



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