HP StorageWorks XP48 Disk Array - Manual (Page 65)

Working With OS-Based Constraints 65
4-4-6 Setting the Unit of Volume Management
In Provisioning Manager, the unit of volume management is an LU or a volume group. If you need to manage
volumes in smaller units, use an OS command or a volume manager command to manually create or expand a
file system or a device file.
There is a one-to-one correspondence between volume groups and volumes. The volume group is used only
for online expansion of a newly created volume. When adding a volume (LU) to a volume group, or deleting a
logical volume, make sure that you specify the volumes and physical partitions, and also specify the priority in
the order they are to be used. In this case, all the command options must be set to the default setting values.
4-4-7 Improving AIX ® Host Performance
Provisioning Manager uses the AIX ® default settings except for the ones described in 4-4-3 , Restrictions on
creating a file system and device file. When you want to improve host performance, manually adjust the
settings.
4-4-8 Using the Volume Manager RAID Functionality
You cannot configure RAID by using Provisioning Manager. Use either of the following methods to configure
RAID:
• Configure RAID by using the functionality of the storage subsystem.
• Configure such RAID software as stripe volume and mirror volume software by manually executing
commands such as the ones for the volume manager.
4-4-9 About the big vg Format Volume Group
If you want to use a special volume group (big vg format) that can handle more volumes, and create more
logical volumes than the default setting, use the OS command to create it manually.
Normally, you can only create the volume group according to the specified option. This volume group can
contain up to 32 physical volumes, and 255 logical volumes.
4-4-10 About Fragment and Data Compression (Saving Disk Space)
When creating many small size files (for example, files of several tens of kilobytes), reducing the fragment size
of the file system can save the disk space but the duration of file system operations might increase.
The following value is specified by default as the file system fragment size:
• JFS: 4,096 bytes
When you want to create a file system with a fragment size different from the default, manually change the
setting for the fragment size, and then create the file system.
4-4-11 About Creating a Logical Volume for the JFS Log
In Provisioning Manager, log files are created in the same volume group by default using the file system
creation command. The JFS log, however, is created on a disk separate from the file system disk to improve
the reliability and capability of the system. To create a logical volume for the JFS log, manually perform
configuration.
4-4-12 Changing the Size of the Logical Volume for the JFS Log
In Provisioning Manager, the log size for one logical partition is 128 MB by default. Change the log size of the
logical volume for the JFS log as necessary.
4-4-13 Changing the File System Check at Startup Setting
Provisioning Manager specifies that the file system is to be checked at system startup after a file system is
created. To change this setting, manually change the setting specified in the information file for the file system,
such as /etc/filesystems, /etc/vfstab.
Depending on the cluster management software, if a standby configuration is used and this setting is specified
so that the file system is checked at startup, it may take time to switch the server when an error occurs. To
avoid this, the setting must be changed so that the file system check is not performed at startup. For details,
see the documentation for the relevant cluster management software.