Installing a DIMM

Use this information to install a DIMM.

About this task

This component can be installed as an optional device or as a CRU. The installation procedure is the same for the optional device and the CRU.

After you install or remove a DIMM, you must change and save the new configuration information by using the Setup utility. When you turn on the compute node, a message indicates that the memory configuration has changed. Start the Setup utility and select Save Settings (see Using the Setup utility for more information) to save changes.

If you are installing a DIMM as a result of a DIMM failure, you might have to reenable the DIMM. To re-enable the DIMM, complete the following steps:

1. Verify that the amount of installed memory is the expected amount of memory through the operating system, by watching the monitor as the compute node starts, by using the CMM sol command, or through IBM Flex System Manager management software (if installed).
   • For more information about the CMM sol command, see the IBM Flex System Chassis Management Module: Command-Line Interface Reference Guide.
   • For more information about IBM Flex System Manager management software, see the IBM Flex System Manager Software: Installation and Service Guide.
2. Run the Setup utility to reenable the DIMMs (see Using the Setup utility for more information).

The compute node has a total of 24 dual inline memory module (DIMM) connectors. The compute node supports low-profile (LP) DDR3 DIMMs with error-correcting code (ECC) in 2 GB, 4 GB, 8 GB, 16 GB, and 32 GB capacities.

The following illustration shows the system-board components, including the DIMM connectors.

The memory is accessed internally through four channels. Each memory channel has three DIMM connectors for each microprocessor (six total). Each channel can have a maximum of eight ranks. The following table lists the memory channels and shows which DIMM connectors are in the channel for each microprocessor.

Table 1. Memory-channel configuration

Microprocessor	Memory channel	DIMM connectors
Microprocessor 1	Channel A	4, 5, and 6
	Channel B	1, 2, and 3
	Channel C	7, 8, and 9
	Channel D	10, 11, and 12
Microprocessor 2	Channel A	22, 23, and 24
	Channel B	19, 20, and 21
	Channel C	13, 14, and 15
	Channel D	16, 17, and 18

Depending on the memory mode that is set in the Setup utility, the compute node can support a minimum of 2 GB and a maximum of 384 GB of system memory in a compute node with one microprocessor. If two microprocessors are installed, the compute node can support a minimum of 4 GB and a maximum of 768 GB of system memory.

The following notes describe information that you must consider when you install memory:

• Maximum DIMM capacity:
  • Registered DIMMs (RDIMMs): 384 GB (using 16 GB RDIMMs)
  • Unbuffered DIMMs (UDIMMs): 128 GB (using 8 GB UDIMMs)
  • Load Reduced DIMMs (LRDIMMs): 768 GB (using 32 GB LRDIMMs)
• RDIMM sizes supported (GB): 2, 4, 8, 16, 32
• UDIMM sizes supported (GB): 2, 4, 8
• LRDIMM sizes supported (GB): 16, 32
• You cannot mix UDIMMs, RDIMMs and LRDIMMs in the same compute node.
• You cannot mix RDIMMs and LRDIMMs in the same compute node.
• A total of eight ranks on each channel is supported.
• If a quad-rank DIMM is installed, install it in the connector at the end of the memory channel.
• If a channel has one or more quad-rank DIMMs, only two DIMMs per channel is supported.
• If you install LRDIMMs in a 3 DIMM per channel configuration, performance might be reduced compared to standard DIMMs.

There are three memory modes:

• Independent-channel mode: Independent-channel mode provides a maximum of 384 GB of usable memory with one installed microprocessor, and 768 GB of usable memory with two installed microprocessors (using 32 GB DIMMs).
• Rank-sparing mode: In rank-sparing mode, one memory DIMM rank serves as a spare of the other ranks on the same channel. The spare rank is held in reserve and is not used as active memory. The spare rank must have identical or larger memory capacity than all the other active DIMM ranks on the same channel. After an error threshold is surpassed, the contents of that rank is copied to the spare rank. The failed rank of DIMMs is taken offline, and the spare rank is put online and used as active memory in place of the failed rank.
  The following notes describe additional information that you must consider when you select rank-sparing memory mode:

  • Rank-sparing on one channel is independent of the sparing on all other channels.
  • You can use the Setup utility to determine the status of the DIMM ranks.
• Mirrored-channel mode: In mirrored-channel mode, memory is installed in pairs. Each DIMM in a pair must be identical in size and architecture. The channels are grouped in pairs with each channel receiving the same data. One channel is used as a backup of the other, which provides redundancy. The memory contents on channel B are duplicated in channel C, and the memory contents of channel A are duplicated in channel D. The effective memory that is available to the system is only half of what is installed.

One DIMM for each microprocessor is the minimum requirement. However, for optimal performance, install DIMMs in sets of four so that you distribute memory equally across all four channels. If two microprocessors are installed, distribute memory across all channels and equally between the microprocessors.

Install DIMMs in order as indicated in the following table for independent-channel mode.

Table 2. DIMM population sequence for independent-channel mode

Number of installed DIMMs	1 microprocessor installed		2 microprocessors installed
	DIMM slot number	DIMMs per channel	DIMM slot number	DIMMs per channel
1	4	1	4	1
2	1		24
3	9		1
4	12		21
5	5	2	9
6	2		13
7	8		12
8	11		16
9	6	3	5	2
10	3		23
11	7		2
12	10		20
13	Not used - maximum of 12 DIMMs in systems with 1 microprocessor		8
14			14
15			11
16			17
17			6	3
18			22
19			3
20			19
21			7
22			15
23			10
24			18

Install DIMMs in order as indicated in the following table for rank-sparing mode.

Table 3. DIMM population sequence for rank-sparing mode

DIMM pair installation order	2 DIMMs per channel		3 DIMMs per channel
	1 microprocessor installed	2 microprocessors installed	1 microprocessor installed	2 microprocessors installed
1	4 and 5	4 and 5	4, 5, and 6	4, 5, and 6
2	8 and 9	20 and 21	7, 8, and 9	19, 20, and 21
3	1 and 2	8 and 9	1, 2, and 3	7, 8, and 9
4	11 and 12	16 and 17	10, 11, and 12	16, 17 and 18
5	n/a	1 and 2	n/a	1, 2, and 3
6		23 and 24		22, 23, and 24
7		11 and 12		10, 11, and 12
8		13 and 14		13, 14, and 15

Install DIMMs in order as indicated in the following table for mirrored-channel mode.

Table 4. DIMM population sequence for mirrored-channel mode

DIMM pair	1 microprocessor installed		2 microprocessors installed
	DIMM slot numbers	DIMMs per channel	DIMM slot numbers	DIMMs per channel
1	4 and 11	1	4 and 11	1
2	9 and 121		21 and 241
3	2 and 51	2	9 and 121
4	8 and 11		13 and 161
5	3 and 61	3	2 and 51	2
6	7 and 101		20 and 231
7	none		8 and 111
8	none		14 and 171
9	none		3 and 61	3
10	none		19 and 221
11	none		7 and 101
12	none		15 and 181
For mirrored-channel mode, the DIMM pair must be identical in size, type, and rank count.

To install a DIMM, complete the following steps:

1. Remove the cover (see Removing the compute node cover).
2. Read the documentation that comes with the DIMM.
3. Remove the air baffle installed over the DIMM connector.
   
4. Locate the DIMM connectors (see System-board connectors). Determine in which DIMM connector you want to install the DIMM.
5. Touch the static-protective package that contains the DIMM to any unpainted metal surface on the IBM Flex System chassis or any unpainted metal surface on any other grounded rack component in the rack in which you are installing the DIMM for at least 2 seconds; then, remove the DIMM from its package.
   
6. Make sure that both retaining clips on the DIMM connector are in the open position.
7. Turn the DIMM so that the DIMM keys align correctly with the DIMM connector on the system board.
   Attention: To avoid breaking the retaining clips or damaging the DIMM connector, handle the clips gently.
8. Press the DIMM into the DIMM connector. The retaining clips lock the DIMM into the connector.
9. Make sure that the small tabs on the retaining clips engage the notches on the DIMM. If there is a gap between the DIMM and the retaining clips, the DIMM has not been correctly installed. Press the DIMM firmly into the connector, and then press the retaining clips toward the DIMM until the tabs are fully seated. When the DIMM is correctly installed, the retaining clips are parallel to the sides of the DIMM.
   
10. Install the air baffle over the DIMM connector.
    Attention: To maintain proper system cooling, do not operate the compute node without air baffles installed over the DIMM connectors.