> -----Original Message-----
> From: Justin Piszcz [mailto:jpiszcz@...]
> Sent: Monday, December 22, 2008 10:25 AM
> To: David Lethe
> Cc: linux-raid@...; smartmontools-
> Subject: RE: Spread Spectrum (SSC) Enable or Disable?
> On Mon, 22 Dec 2008, David Lethe wrote:
> >> -----Original Message-----
> >> From: linux-raid-owner@... [mailto:linux-raid-
> >> owner@...] On Behalf Of Justin Piszcz
> >> Sent: Monday, December 22, 2008 7:59 AM
> >> To: linux-raid@...
> >> Cc: smartmontools-support@...
> >> Subject: Spread Spectrum (SSC) Enable or Disable?
> >> Besides the power supply/surge/etc with a lot of drives-- I have
> >> http://www.wrightthisway.com/Articles/cat_reviews.html
> >> "As I mentioned earlier, the enclosure will definitely handle
> >> using Spread Spectrum Clocking (SSC), an increasingly common
> >> that helps reduce electromagnetic interference, especially between
> >> drives in close proximity with each others, such as you might have
> > a
> >> RAID setup, so that is a definite plus here."
> >> With 16-24 disks-- if they are close together, it sounds like a
> >> idea to use Spread Spectrum Clocking?
> >> Does anyone here with a large-ish raid array use this?
> >> Any enterprise-insiders care to comment?
> >> Justin.
> >> --
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> > I know for a fact that Xyratex supports SSC on SOME of their
> > However,
> > there is a caveat to be aware of ... some RAID
> > controllers/firmware/enclosure combinations
> > have problems "seeing" disks that have SSC enabled. Don't just turn
> > this on unless you
> > verify with the enclosure manufacturer that they support SSC for
> > desired combination.
> > David
> Dave, thanks for the reply, in my case (and most people on this list)
> their arrays in a regular ATX/case.
> The question I had was:
> "especially between drives in close proximity with each others, such
> you might have in a RAID setup, so that is a definite plus here"
> Besides the staggered spin-up functionality (which is enabled, at
> least with WD drives when you enable SSC, which is good for the PSU)
> there any other 'benefit' to using SSC in relation to the comment of
> drives being close to one another?
> e.g., have studies been done looking at several raid arrays with ssc
> enabled vs. disabled and what / if any correlation can be made within
> respect to failure rates?
I can't imagine it having any positive effect.
SSC has to do with reducing overall electromagnetic emissions (EMI) for
FCC cert by
spreading around clock harmonics a few MHz.
All the drive vendors run reliability testing in the more expensive,
enclosures for a reason. Torque/Vibration kills data, so they know they
I view SSC as a cheat code that enables them to pass the FCC tests by
which will save them some money, and make a less reliable, more
I avoid any enclosure/RAID vendor that advertizes SSC as a requirement
is different). This lets them get away with selling something a little
therefore, less reliable, then what they would normally have to sell to
meet FCC certs.
If I was in market for low-cost enclosures, I would see if they ran
their FCC compliance
testing with SSC enabled. If they did, don't buy their enclosure.