SSD drives

[Baruch Siach]

Hi Oleg,

On Sun, Dec 30, 2012 at 10:40:31AM +0200, Oleg Goldshmidt wrote:
> On Sun, Dec 30, 2012 at 8:46 AM, shimi <linux-il at shimi.net> wrote:
> > I really don't think so. SSDs (IMHO) makes computer much faster due to the
> > VERY low seek time - the time it takes you to get a block. Compare 10-20ms
> > with ~0.1ms. A regular hard drive simply wastes a lost of time seeking the
> > data, instead of... reading it :)
> 
> Absolutely correct. However, there is a tiny fraction of the seek time
> that is not always a waste, and I think it is worth mentioning. There
> is, I believe, a consideration that is usually overlooked when SSDs
> are considered for server use, including a "desktop" that is used as a
> server, which is why I am mentioning it here. In a server, magnetic
> disk rotation - or, rather the air turbulence generated between the
> rotating disk and its enclosure - is the only source of entropy that
> makes random numbers random (seek times have a tiny random component
> due to the turbulence, and it is captured). This does not apply to
> SSDs, and as a result your security may be compromised (attacks
> exploiting not very random RNGs are well known).

Recent Intel CPUs introduced the RDRAND instruction that is essentially a 
Random Number Generator. Recent kernels (v3.2 and later) added support for 
this instruction. See http://git.kernel.org/linus/628c6246d4. See also the 
related commit (from v3.6) at http://git.kernel.org/linus/c2557a303 (and note 
the funny commit log).

These patches were backported to all supported stable kernel trees (back to 
v2.6.32).

> In a laptop or a desktop entropy is also generated by keyboard and
> mouse (which may or may not be good enough). In a server that hardly
> applies.

baruch

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