> -----Original Message----- > From: Justin Piszcz [mailto:jpiszcz@xxxxxxxxxxxxxxx] > Sent: Monday, December 22, 2008 10:25 AM > To: David Lethe > Cc: linux-raid@xxxxxxxxxxxxxxx; smartmontools- > support@xxxxxxxxxxxxxxxxxxxxx > Subject: RE: Spread Spectrum (SSC) Enable or Disable? > > > > On Mon, 22 Dec 2008, David Lethe wrote: > > > > > > >> -----Original Message----- > >> From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid- > >> owner@xxxxxxxxxxxxxxx] On Behalf Of Justin Piszcz > >> Sent: Monday, December 22, 2008 7:59 AM > >> To: linux-raid@xxxxxxxxxxxxxxx > >> Cc: smartmontools-support@xxxxxxxxxxxxxxxxxxxxx > >> Subject: Spread Spectrum (SSC) Enable or Disable? > >> > >> Besides the power supply/surge/etc with a lot of drives-- I have > read: > >> > >> http://www.wrightthisway.com/Articles/cat_reviews.html > >> "As I mentioned earlier, the enclosure will definitely handle drives > >> using Spread Spectrum Clocking (SSC), an increasingly common feature > >> that helps reduce electromagnetic interference, especially between > >> drives in close proximity with each others, such as you might have > in > > a > >> RAID setup, so that is a definite plus here." > >> > >> With 16-24 disks-- if they are close together, it sounds like a good > >> idea to use Spread Spectrum Clocking? > >> Does anyone here with a large-ish raid array use this? > >> > >> Any enterprise-insiders care to comment? > >> > >> Justin. > >> -- > >> To unsubscribe from this list: send the line "unsubscribe linux- > raid" > >> in > >> the body of a message to majordomo@xxxxxxxxxxxxxxx > >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > I know for a fact that Xyratex supports SSC on SOME of their > enclosures. > > 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 your > > desired combination. > > > > David > > Dave, thanks for the reply, in my case (and most people on this list) > use > their arrays in a regular ATX/case. > > The question I had was: > > "especially between drives in close proximity with each others, such as > 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) is > 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? > > Justin. 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, heavy-gauge metal enclosures for a reason. Torque/Vibration kills data, so they know they need rigidity. I view SSC as a cheat code that enables them to pass the FCC tests by removing shielding which will save them some money, and make a less reliable, more error-prone enclosure. I avoid any enclosure/RAID vendor that advertizes SSC as a requirement (compliance/support is different). This lets them get away with selling something a little more flimsy, 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. David -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
