IBM Power7 Optimization And Tuning Manual page 215

– Paging space: Configure the paging space to include at least the following items:
• Place paging spaces on dedicated disks to eliminate I/O contention.
• Use multiple paging spaces that are spread across multiple disks.
• Make the primary paging space hd6 a little bigger than the secondary
paging spaces.
• Ensure that the paging space is sufficient to support the number of concurrent SAS
processes, because the number of SAS processes can be dynamic, depending on
application workload.
– Volume groups (VGs): Use the AIX Scalable or Big volume group.
The scalable VG implementation provides configuration flexibility regarding the number
of physical volumes (PVs) and logical volumes (LVs) that an instance of the new VG
type can accommodate. The configuration options allow any scalable VG to contain 32,
64, 128, 256, 512, 768, or 1024 disks and 256, 512, 1024, 2048, or 4096 LVs. You do
not need to configure the maximum values of 1024 PVs and 4096 LVs when you create
the VG to account for potential future growth. You can increase the initial settings later,
as required.
– Disk layout: Minimize disk contention between SAS temporary space and data spaces
by considering the following items:
• Avoid disk contention by placing SAS temporary-space file systems and SAS data
file systems on physically separate disks.
• Use multiple storage-server controllers to further separate and isolate the I/O traffic
between SAS temporary and data spaces.
• Use multiple mount points for SAS file systems. Place the operating system, SAS
installation, SAS user, SAS temporary space, and SAS data file systems on
separate physical disks.
• Consider creating multiple SAS WORK areas that are used by groups of
SAS users.
• Create separate JFS2 log files on separate physical disks for each SAS file system.
• Spread the I/O workload across many physical disk spindles rather than across
fewer, larger-capacity disks. Determine the sizing, based on the quantity of disks
rather than on disk capacity. Do not wrap logical unit numbers (LUNs) around the
same spindle sets.
• Do not share disk spindles with a relational database management system
(RDBMS).
– Release-behind mechanism for JFS2: This feature allows the file system to release the
file pages from file system buffer cache when an application reads or writes the file
pages. This feature helps when the SAS application performs a great deal of
sequential reads or writes, and after the file pages are accessed, they are not
accessed again soon. This feature can be configured on a file system basis. When you
use the mount command, enable release-behind by specifying one of the
following flags:
• Release-behind sequential read flag (-rbr),
• Release-behind sequential write flag (-rbw),
• Release-behind sequential read and write flag (-rbrw).
Appendix C. POWER7 optimization and tuning with third-party applications
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