Whether an LPAR should use dedicated memory or shared memory can be decided when creating an LPAR using the mem_mode attribute. The attribute mem_mode can have one of the following two values:

mem_mode : memory mode
ded - dedicated memory
shared - shared memory

We create the LPAR shlpar1 with shared memory. As with dedicated memory, the min_mem, desired_mem and max_mem attributes can be used to specify how much memory the LPAR should have at least, normally (desired) and at most.

$ lpar -m ms03 create shlpar1 mem_mode=shared desired_mem=4G max_mem=8G
    > shlpar1
$

Checking the profile standard shows that an LPAR with shared memory was created. The primary paging virtual I/O server is ms03-vio1:

$ lpar -p standard lsmem shlpar1
             MEMORY           MEMORY             HUGE_PAGES           MEM         PAGING_VIOS        
LPAR_NAME  MODE    AME  MIN   DESIRED  MAX   MIN   DESIRED  MAX   IO_ENTITLED  PRIMARY    SECONDARY
shlpar1    shared  0.0  1024  4096     8192  null  null     null  auto         ms03-vio1  -
$

However, creating an LPAR with shared memory does not automatically assign a paging device, as the output of “ms lspgdev” shows:

$ ms lspgdev ms03
                                                                  REDUNDANT
MS_NAME  DEVICE_NAME  PAGING_VIOS_NAME  STATE     DEVICE_NAME  PAGING_VIOS_NAME  STATE  SIZE   TYPE  LPAR_ID
ms03     hdisk4       ms03-vio1         Inactive  -            -                 -      51200  phys  none
ms03     hdisk3       ms03-vio1         Inactive  -            -                 -      51200  phys  none
$

No paging device has yet been assigned to one of the LPARs (column LPAR_ID). Next, we therefore activate the LPAR using the profile standard:

$ lpar -p standard activate shlpar1
hmc01: chsysstate -m ms03 -r lpar -o on -n shlpar1 -f standard
ERROR: remote HMC command returned an error (1)
StdErr: HSCLA457 Partition shlpar1(6) cannot be activated because its profile is missing a necessary virtual I/O adapter. Shared memory partitions are required to have at least one virtual I/O adapter of any type other than virtual serial.
$

Unfortunately, it doesn’t work that way yet. We created the LPAR shlpar1 without a virtual adapter, but the following two conditions apply in order to use of shared memory:

• • A shared memory LPAR must not have any physical I/O adapters.
  • A shared memory LPAR must have at least one virtual adapter (apart from the two standard virtual serial adapters).

We add a virtual ethernet adapter in slot 2 in order be able to activate the LPAR:

$ lpar -p standard addeth shlpar1 2 900
$

(The last argument is the PVID of the virtual Ethernet adapter, but is irrelevant here because it is not used.)

Activation of the LPAR is now successful:

$ lpar -p standard activate shlpar1
$

Now one of the two paging devices is also assigned, as the output of “ms lspgdev” indicates:

$ ms lspgdev ms03
                                                                  REDUNDANT
MS_NAME  DEVICE_NAME  PAGING_VIOS_NAME  STATE     DEVICE_NAME  PAGING_VIOS_NAME  STATE  SIZE   TYPE  LPAR_ID
ms03     hdisk4       ms03-vio1         Inactive  -            -                 -      51200  phys  none
ms03     hdisk3       ms03-vio1         Active    -            -                 -      51200  phys  6
$

According to the output, hdisk3 was assigned as a paging device. The selection is made automatically by the hypervisor. An available paging device, which has at least the max_mem capacity of the LPAR, is selected. This ensures that theoretically even the entire memory of the LPAR could be paged out to the paging device. This does not happen, however, as a minimum amount of main memory, dependent on the LPAR, is always allocated.