Removal and replacement procedures 61
Online spare memory
Online spare memory provides a higher level of memory protection than Advanced ECC ("Advanced
ECC memory" on page 60). With online spare memory, the probability of a server failing because of
uncorrectable memory errors is reduced.
In this mode, degraded memory that is receiving a high rate of correctable memory errors is automatically
disengaged and a replacement set of memory is used in its place. Because DIMMs that are receiving a
high rate of correctable memory errors have an increased probability of receiving an uncorrectable
memory error (which results in a server failure), the server experiences higher availability. The degraded
memory can be replaced during scheduled downtime and poses no additional risk to the server.
Online spare memory is supported with one to four memory boards installed. On this server, each
installed memory board is protected by its own spare memory. No operating system support is required.
The following guidelines apply to online spare memory:
• All general memory requirements apply.
• Online spare memory supports 1, 2, 3, or 4 memory boards.
• Each board must have a valid online spare configuration. No dependencies exist for the
configuration between different memory boards.
• Each memory board includes its own online spare bank. All boards will operate in online spare
memory mode independently. Each board can failover to its online spare bank independent of the
other memory boards. Some boards can be in degraded online spare mode while others are still in
operational online spare memory mode.
• The minimum valid online spare configuration for a memory board requires at least one bank of
dual-rank DIMMs or two banks of single-rank DIMMs. If the server does not meet these requirements,
an error message appears during POST and the server defaults to Advanced ECC ("Advanced ECC
memory" on page 60).
• The server automatically configures the optimal online spare solution.
• Hot-plug operations are not supported.
HP recommends the following configurations. These configurations result in optimal use of memory. Other
configurations are valid, but do not result in the maximum amount of installed memory being available to
the operating system.
• If only single-rank DIMMs are used on a memory board, all DIMMs should be of the same size on
that memory board.
• If only dual-rank DIMMs are used on a memory board, all DIMMs should be of the same size on that
memory board.
• If a mixture of single- and dual-rank DIMMs are used on a memory board, the dual-rank DIMMs
should be twice the size of any single-rank DIMM.
After installing DIMMs, use RBSU to configure the server ("Configuring the memory" on page 63) for
online spare memory support.
Hot-plug mirrored memory
Hot-plug mirrored memory provides a higher level of memory protection than either Advanced ECC
("Advanced ECC memory" on page 60) or online spare memory (on page 61). With hot-plug mirrored
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