Conseils extrait du redbook : IBM eServer Certification Study Guide - pSeries AIX System Administration.

Default paging space (hd6) size

1. Paging space can use no less than 16 MB, except for hd6. In AIX Version 4.2.1, hd6 can use no less than 32 MB, and in AIX Version 4.3 and later, no less than 64 MB.
2. Paging space can use no more than 20 percent of the total disk space.
3. If real memory is less than 256 MB, paging space is two times real memory.
4. If real memory is greater than or equal to 256 MB, paging space is 512 MB.

Placement of paging spaces

To improve paging performance, you should use multiple paging spaces and locate them on separate physical volumes whenever possible. More than one paging space can be located on the same physical volume, however, we do not recommend it.

Sizes of paging spaces

The general recommendation is that the sum of the sizes of the paging spaces should be equal to at least twice the size of the real memory of the machine, up to a memory size of 256 MB (512 MB of paging space). For memories larger than 256 MB, the following rule is recommended:

     Total paging space = 512 MB + (memory size - 256 MB) * 1.25

Ideally, there should be several paging spaces of roughly equal size each on a different physical disk drive. If you decide to create additional paging spaces, create them on physical volumes that are more lightly loaded than the physical volume in rootvg.

While the system is booting, only the primary paging space (hd6) is active. Consequently, all paging-space blocks allocated during boot are on the primary paging space. This means that the primary paging space should be somewhat larger than the secondary paging spaces. The secondary paging spaces should all be of the same size to ensure that the round-robin algorithm can work effectively.

The lsps -a command provides a snapshot of the current utilization of each of the paging spaces on a system, while the lsps -s command provides a summary of the total active paging space and its current utilization.

Limitations of volume groups having paging space

Avoid adding paging space to the volume groups on portable disks in systems prior to AIX 5L Version 5.1. Removing a disk that is online with an active paging space will require a reboot to deactivate the paging space and, therefore, cause user disruption.

Note: In versions prior to AIX 5L Version 5.1, a volume group that has a paging space volume on it cannot be varied off or exported while the paging space is active. Before deactivating a volume group having an active paging space volume, ensure that the paging space is not activated automatically at system initialization and then reboot the system.

Managing paging spaces

The following commands are used to manage paging space:

chps Changes the attributes of a paging space.
lsps Displays the characteristics of a paging space.
mkps Creates an additional paging space.
rmps Removes an inactive paging space.
swapon Activates a paging space.
swapoff Deactivates one or more paging spaces.

Moving the hd6 paging space to another volume group

Moving a paging space with the name hd6 from rootvg to another volume group is not recommended because the name is hard-coded in several places.

Only the paging spaces in rootvg will be active during the second phase of the boot process, and having no paging space in rootvg could severely affect system boot performance. If you want the majority of paging space on other volume groups, it is better to make hd6 as small as possible (the same size as physical memory) and then create larger paging spaces on other volume groups.