[linux-elitists] A modest proposal: SSD disk acceleration in kernel.

Ruben Safir ruben@mrbrklyn.com
Fri Oct 24 12:20:54 PDT 2008


On Fri, Oct 24, 2008 at 01:29:51PM -0400, Bill Bogstad wrote:
> On Fri, Oct 24, 2008 at 11:26 AM, Karsten M. Self
> <karsten@linuxmafia.com> wrote:
> > on Fri, Oct 24, 2008 at 10:58:40AM -0400, Ruben Safir (ruben@mrbrklyn.com) wrote:
> 
> >> BBad idea with current SSD's bcause of limited life.
> >
> > See Linus's blog entry (referenced in OP) for specifics on SSD lifetimes
> > and MTBF.  The evidence there is that it's at least comperable to
> > rotational media.  I'm guessing with sufficient error detection and
> > correction and allowing for degraded volume, probably better.
> 
> I'm wondering just how different the failure modes will be as well.
> Certainly if we are talking about 'wear' effects it will.  With
> spinning platters, it is common wisdom that if you start getting new
> bad blocks you should plan on replacement or catastrophic failure
> soon.  Flash memory blocks which have reached their max. erase cycle
> limit wouldn't seem to imply the same thing.  OTOH, this would also
> seem to imply that SSD interfaces that hide these kinds of issues
> behind disk-like interfaces aren't good for reliable systems.  Does
> the ATA/SATA command set have a way to inform the host that it only
> has N writes left on the 'disk'?
> 
> OTOH,  it's my understanding that flash is laid out in a row/column
> format at lot like RAM.  I suppose if the access electronics go bad,
> you could lose the
> equivalent of a 'track' of data all at once....
> 


I' going to have to go to school on the flash drive but what limits the
number of erase cycles that a flash can do?

Ruben

> Bill Bogstad
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