Installation guide

12 IBM Eserver xSeries 366 Technical Introduction
A more detailed description and the exact sequence for installation can be found in the
xSeries 366 User’s Guide.
򐂰 If you want to install the full 64 GB, you must remove the existing 1 GB DIMMs and fully
populate the x366 with four memory cards, each with four 4 GB DIMMs.
Several advanced features are implemented in the x366 memory subsystem, collectively
known as
Active Memory:
򐂰 Memory ProteXion
The Memory ProteXion feature (also known as
redundant bit steering) provides the
equivalent of a hot-spare drive in a RAID array. It is based in the memory controller, and it
enables the server to sense when a chip on a DIMM has failed and to route the data
around the failed chip.
Normally, 128 bits out of every 144 are used for data and the remaining 16 bits are used
for ECC functions. However, the x366 needs only 12 bits to perform the same ECC
functions, thus leaving 4 bits free. These 4 bits are equivalent to an x4 memory chip on the
DIMM, which Memory ProteXion uses. In the event that a chip failure on the DIMM is
detected by memory scrubbing, the memory controller can re-route data around that failed
chip through these spare bits.
It can do this automatically without issuing a Predictive Failure Analysis® (PFA) or light
path diagnostics alert to the administrator (although an event is logged to the service
processor log). After the second DIMM failure, PFA and light path diagnostics alerts would
occur on that DIMM as normal.
򐂰 Memory scrubbing
Memory scrubbing is an automatic daily test of all of the system memory that detects and
reports memory errors that might be developing before they cause a server outage.
Memory scrubbing and Memory ProteXion work in conjunction with each other and do not
require memory mirroring to be enabled to work properly.
When a bit error is detected, memory scrubbing determines whether the error is
recoverable. If it is recoverable, Memory ProteXion is enabled and the data that was stored
in the damaged locations is rewritten to a new location. The error is then reported so that
preventive maintenance can be performed. As long as there are enough good locations to
allow the proper operation of the server, no further action is taken other than recording the
error in the error logs.
If the error is not recoverable, then memory scrubbing sends an error message to the light
path diagnostics, which turns on the proper lights and LEDs to guide you to the damaged
DIMM. If memory mirroring is enabled, then the mirrored copy of the data from the
damaged DIMM is used until the system is powered down and the DIMM is replaced.
򐂰 Memory mirroring
Memory mirroring is roughly equivalent to RAID-1 in disk arrays, in that usable memory is
halved and a second copy of data is written to the other half. If 8 GB is installed, then the
operating system sees 4 GB when memory mirroring is enabled. (It is disabled in the BIOS
Note: In BIOS, there is a Memory Array setting in Advanced Settings. When it is set to
High Performance Memory Array, BIOS reconfigures the server for maximum
performance at the expense of some fault tolerance features, including Memory
ProteXion. For a production environment, we recommend that you do not select this
setting, thereby keeping your system protected from memory failures with Memory
ProteXion.