Mirrored Memory - HP ProLiant ML370 G5 User Manual

•
When only bank A on any memory board is populated, it must be fully populated with dual-rank
FBDIMMs.
•
For dual memory board configurations, each memory board must have a valid online spare FBDIMM
configuration. It is supported to have memory board 2 unpopulated while memory board 1 has a
valid online spare configuration.
•
For optimum memory usage, HP recommends all DIMMs on a memory board be the same size with
the same HP part number. If different sized DIMMs are used on a memory board, a portion of the
installed memory may not be utilized.
•
For dual memory board configurations, the FBDIMM part numbers on memory board 1 are not
required to match those installed on memory board 2
In online spare mode, each installed memory board must have an FBDIMM configuration as specified in
the following table:
Online spare memory configurations (per memory board):
Memory board
configuration
1
2
3
4
* Bank A must be populated with dual-rank FBDIMMs to support these configurations.
After installing FBDIMMs, use RBSU to configure the system for online spare memory support
("Configuring online spare

Mirrored memory

Mirroring provides protection against uncorrectable memory errors that would otherwise result in server
downtime. This protection is available without any operating system support.
Mirroring is performed on the memory board level. Memory board 1 and memory board 2 mirror each
other.
Each memory board maintains a copy of all memory contents. Memory writes go to both memory boards.
Memory reads come from only one of the two memory boards (unless an uncorrectable error occurs). If a
memory read on one memory board returns incorrect data due to an uncorrectable memory error, the
system automatically retrieves the proper data from the other memory board. A memory board is not
necessarily disabled (thus losing mirroring protection) because of a single uncorrectable error. Mirroring
protection is not lost due to transient and soft uncorrectable errors, resulting in systems that maintain
mirroring protection (and thus improved uptime) unless there is a true FBDIMM failure.
Because both memory boards are active, concurrent reads from both memory boards at the same time are
possible. Therefore, mirroring provides superior read performance compared to all other Advanced
Memory Protection modes.
Mirrored memory allows the server to keep two copies of all memory data on separate memory boards. If
an uncorrectable error is encountered, the proper data is retrieved from the memory board that does not
contain the error. There is no negative performance impact from using mirrored memory.
In addition to general configuration requirements
mirrored memory has the following FBDIMM configuration requirements:
•
Memory board 1 and memory board 2 must both be populated.
•
Memory board 1 and memory board 2 must have identical memory configurations.
Bank A Bank B
1A and 5A* 2B and 6B
X —
X X
X X
X X
memory" on page 80).
Bank C
3C and 7C
—
—
X
X
("FBDIMM installation guidelines" on page 47),
Bank D
4D and 8D
—
—
—
X
Hardware options installation 44