Installation guide

14 IBM Eserver xSeries 366 Technical Introduction
To understand what memory mirroring and hot-swap capabilities exist with the server, you
must first understand how the memory cards are powered. The x366 has two separate
memory power buses that are split between the four memory cards. As shown in Figure 9,
memory cards 1 and 2 are on power bus 1, and memory cards 3 and 4 are on power bus 2.
Figure 9 Memory hardware on the x366
Mirroring takes place across the two power buses. In other words, the memory DIMMs in
cards 1 and 2 are mirrored to the memory DIMMs in cards 3 and 4. With memory mirroring
enabled in BIOS, you can hot-swap one memory card at a time on each memory power bus.
Once memory mirroring is enabled, the data that is written to memory will be stored in two
locations. For read operations, data is read from the DIMMs with the least amount of reported
memory errors through memory scrubbing.
Memory scrubbing is an automatic and regular test of all the system memory that detects and
reports memory errors before they cause a server outage. If memory scrubbing determines
that the DIMM is damaged beyond use, read and write operations are redirected to the
remaining good DIMM. Memory scrubbing then reports the damaged DIMM and the light path
diagnostic displays the error. 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
replaced. After the damaged DIMM is replaced, memory mirroring will copy the mirrored data
back onto the new DIMM.
Key configuration rules relating to memory mirroring are as follows:
򐂰 Memory mirroring must be enabled in the BIOS (it is disabled by default).
򐂰 Both memory cards must have the same total amount of memory, and must have identical
DIMMs. In other words, DIMMs must be installed in matched quads to support memory
mirroring. Partial mirroring is not supported. See the x366 Installation Guide for
information about the exact installation order required.
Hot-swap memory
The x366 supports hot-swap memory, which means that if a DIMM fails, it can be replaced
with a new DIMM without powering down the server. This advanced feature allows for
maximum system availability. Hot-swap memory requires that memory mirroring be enabled.
Four memory cards
(card 1 standard)
Each card has
four DIMM sockets
Card 1 has sockets
1 and 3 filled with
1 GB DIMMs
1
2
3
4
DIMM
Socket 1
DIMM
Socket 4
Hot-swap
enabled LED
Memory port
power LED
Power bus 2
(cards 3 & 4)
Power bus 1
(cards 1 & 2)
Important: Because of memory mirroring, you will only have half of the total amount of
memory available. If 8 GB is installed, for example, then the operating system sees 4 GB
once memory mirroring is enabled (it is disabled in the BIOS by default).