Datasheet

Functional Architecture Intel
®
Server Board S2400GP TPS
Revision 1.01
Intel order number G50295-002
30
When Sparing Mode is operational, for each channel, the largest size memory rank is reserved
as a “spare” and is not used during normal operations. The impact on Effective Memory Size is
to subtract the sum of the reserved ranks from the total amount of installed memory.
Hardware registers count the number of Correctable ECC Errors for each rank of memory on
each channel during operations and compare the count against a Correctable Error Threshold.
When the correctable error count for a given rank hits the threshold value, that rank is deemed
to be “failing”, and it triggers a Sparing Fail Over (SFO) event for the channel in which that rank
resides. The data in the failing rank is copied to the Spare Rank for that channel, and the Spare
Rank replaces the failing rank in the IMC’s address translation registers.
An SFO Event is logged to the BMC SEL. The failing rank is then disabled, and any further
Correctable Errors on that now non-redundant channel will be disregarded.
The correctable error that triggered the SFO may be logged to the BMC SEL, if it was the first
one to occur in the system. That first correctable error event will be the only one logged for the
system. However, since each channel is a Sparing Domain, the correctable error counting
continues for other channels which are still in a redundant state. There can be as many SFO
Events as there are memory channels with DIMMs installed.
3.6.4.3 Mirrored Channel Mode
Channel Mirroring Mode gives the best memory RAS capability by maintaining two copies of the
data in main memory. If there is an Uncorrectable ECC Error, the channel with the error is
disabled and the system continues with the “good” channel, but in a non-redundant
configuration.
For Mirroring mode to be to be available as a RAS option, the DIMM population must be
identical between each pair of memory channels that participate. Not all channel pairs need to
have memory installed, but for each pair, the configuration must match. If the configuration is
not matched up properly, the memory operating mode falls back to Independent Channel Mode.
Mirroring Mode is enabled/disabled in the Memory RAS and Performance Configuration screen
in the <F2> BIOS Setup Utility.
When Mirroring Mode is operational, each channel in a pair is “mirrored” by the other channel.
The impact on Effective Memory size is to reduce by half the total amount of installed memory
available for use.
When Mirroring Mode is operational, the system treats Correctable Errors the same way as it
would in Independent channel mode. There is a correctable error threshold. Correctable error
counts accumulate by rank, and the first event is logged.
What Mirroring primarily protects against is the possibility of an Uncorrectable ECC Error
occurring with critical data “in process”. Without Mirroring, the system would be expected to
“Blue Screen” and halt, possibly with serious impact to operations. But with Mirroring Mode in
operation, an Uncorrectable ECC Error from one channel becomes a Mirroring Fail Over (MFO)
event instead, in which the IMC retrieves the correct data from the “mirror image” channel and
disables the failed channel. Since the ECC Error was corrected in the process of the MFO Event,
the ECC Error is demoted to a Correctable ECC Error. The channel pair becomes a single non-
redundant channel, but without impacting operations, and the Mirroring Fail Over Event is