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Memory sparing mode
In memory-sparing mode, one memory rank serves as a spare for other ranks on the same channel in case
they fail. The spare rank is held in reserve and not used as active memory until a failure is indicated, with
reserved capacity subtracted from the total available memory in the system. The DIMM installation order for
memory sparing varies based on the number of processors and memory modules installed in the server.
After an error threshold is surpassed in a system protected by memory sparing, the content of a failing rank
of DIMMs is copied to the spare rank. The failing rank is then taken offline and the spare rank placed online
for use as active memory in place of the failed rank. Since the failover process involves copying of memory
content, the level of memory redundancy provided by memory sparing is less than that provided by memory
mirroring: memory mirroring is the preferred failure-protection choice for critical applications.
Memory sparing guidelines:
• The spare rank must have identical or larger memory capacity than all of the other active memory ranks on
the same channel.
• This mode only applies to single-rank memory modules. When installing DIMMs consisting of more than
two ranks, including dual-rank, quad-rank or octal-rank memory modules, refer to "Independent memory
mode installation order" on page 154 instead.
With two processors
The following table shows the DIMM population sequence for memory sparing when two processors are
installed.
Table 30. Memory sparing with two processors
Total
DIM-
Ms
1
2
3
4
1
2
3
4
24
With four processors
The following tables show the DIMM population sequence for memory sparing when four processors are
installed.
Table 31. Memory sparing with four processors
Total
DIMMs 1
2
3
4
48
1
2
3
4
Total
DIMMs 25 26 27 28 29 30
25 26 27 28 29 30
48
ThinkSystem SR860 V2Setup Guide
158
Processor 1
5
6
7
8
9
10 11 12
5
6
7
8
9
10 11 12
Processor 1
5
6
7
8
9
10 11 12
5
6
7
8
9
10 11 12
Processor 3
31 32 33 34 35 36
31 32 33 34 35 36
Processor 2
13 14 15 16 17 18
19 20 21 22 23 24
13 14 15 16 17 18
19 20 21 22 23 24
Processor 2
13 14 15 16 17 18
19 20 21 22 23 24 DIMMs
13 14 15 16 17 18
19 20 21 22 23 24
Processor 4
37 38 39 40 41 42
43 44 45 46 47 48 DIMMs
37 38 39 40 41 42
43 44 45 46 47 48
Total
DIMMs
24
Total
48
Total
48
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