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.
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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.
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