On Sat, 17 May 2003, Wolfgang S. Rupprecht wrote:
> >     umass0: LEXR PLUG DRIVE LEXR PLUG DRIVE, rev 1.10/0.01, addr 2
> ...  
> >     rnd: sd1 attached as an entropy source (collecting)
> 
> What is being used as the entropy source?  The data read or the 
> rotational/seek delays?

Timing, and the block addresses used.  See the call to rnd_add_uint32 in
sd.c.

The "rnd: ... attached ... (collecting)" message is printed only
with options RND_VERBOSE, and indicates that it's both "collecting"
and "estimating" entropy.  I'd prefer it to say "(collecting without
estimation)", because I don't have enough trust in the randomness of
timing variations in solid state storage devices.

--apb (Alan Barrett)