On Sat, 20 Sep 2014 20:00:54 -0400, Yousuf Khan
wrote:

On 20/09/2014 8:56 AM, wrote:
I have a PC setup with RAID1 by somebody else.
It has Asus P6T SE board with ICH10R.
Upon booting, the BIOS whinges that a disk is degraded, giving serial
number thereof. Then Windows also pops up a helful alert that disk on
port3 is degraded and that human should replace offending item.

Instead, I went into BIOS and changed SATA settings from RAID to IDE,
then ran Seagate disk toola on both disks. It says SMART is okay for
both, so I ran long diagnostic. Both disk pass.
So maybe I have intermittent fault, either drive or controller?
They have done 33000 hours, so perhaps time for a trade-in...

RAID can and does hiccup from time to time. It's hard to keep the two
disks synchronized all of the time. One might run into a weak sector
(still readable, just requiring more retries), while the other is just
fine, and that looks like a disk going bad to the RAID software. That's
why RAID disks are sold specially designed for RAID, they have higher
tolerances for intermittent timing problems.
I thought the main difference for drives intended for RAID
was that the internal error recovery was
defaulted to time limited techniques, so an error would be returned
in a couple of seconds (or less), rather than after a 5 minute (or
longer) attempt.

Seagate calls this Time-Limited Error Recovery (TLER)
Note that there are several variations on TLER:
. RAID, a couple of seconds in about 2010, if not sure
what now. (The Wikipedia article:

http://www.experts-exchange.com/Secu...hing-Quiz.html
says 7 seconds and user controlled timeouts are also available on
drives.)
. streaming, perhaps on the fly only, but less than a
few disk revolutions in any case

See also:
https://wdc.custhelp.com/app/answers...lack)-and-raid
TLER is discussed


Yousuf Khan