[Discuss] ssd's in linux

[kentborg at borg.org (Kent Borg)]

On 11/08/2013 06:15 AM, Stephen Adler wrote:
> I'm thinking of upgrading my linux system by adding an SSD drive to 
> use as my system disk. Has anyone done this? Any pros and cons 
> regarings using SSD's? I'm more intrested in the cons.

I have been wondering the same thing, I have an empty msata slot in my 
Thinkpad, and little flash cards that fit in there are pretty cheap.  
Especially the small capacity ones: ~60GB for ~70 dollars.

But flash makes me worry.  In the memory stick and SD space they like to 
go from working to not working in an instant, with no warning nor change 
to recover anything.  And recently a Linux kernel release was delayed 
when Linus' fancy SSD volume died--with no warning nor chance to recover 
anything.

What I have been considering is using an SSD as a cache, and in the 3.10 
kernel there is support for this (Bcache).  Given Linus' recent 
experience, I bet it is pretty solid about not leaving data exposed on 
SSD only for too long.  Googling about a bit it seems a different 
dm-cache feature showed up a little before that.

How big is my disk "working set"?  I bet 60GB would cover it pretty 
well.  Bcache only caches random disk access (configurable), which makes 
sense, disks can sustain sequential just fine, which makes 60GB even 
bigger.  It seems Bcache came from Google, where they stack this on top 
of raid arrays.

I use Ubuntu (though I am getting annoyed by it and might switch to 
something else), the recent release is on kernel 3.11, and next April's 
long-term support release presumably would be at least as new a kernel, 
so doing it then might make sense.

I run my disk encrypted, so whatever I might do needs to stack with 
that, too.

-kb