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Volume Group Understanding

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Operating Systems AIX Volume Group Understanding
# 1  
Old 06-28-2006
Volume Group Understanding
Looking for help in understanding volume groups.

On the internal disks is it possible to have other volume groups other then root vg? If so would the other vg be captured in the mksysb?

Any documentation links that you can point me to on volume groups and such woudl be welcomed.

Thanks
# 2  
Old 06-29-2006
A volume group is a logical collection of "disks" and is the basic building block of logical storage in AIX. A volume group (VG) can span multiple disks, whether internal or external disks. External disks would typically SAN but could be external SCSI or probably other types too (perhaps even a USB key!) since AIX volume groups are a solid abstraction layer that allows you not to care too much about the hardware underlying the volume group. Unless of course you are the sysadmin such as myself whose day has now stretched to 15 #@*&!!! hours migrating LPARs from one machine to another, snagged by IBM's LVM layer in one setback of many.

Anyways, you can use internal disks for VG's other than rootvg, you can create any kind of user VG that you like on internal or external disks. In fact, rootvg itself doesn't need to reside on internal disk either, you can create the rootvg on a SAN disk as well, or create one that is mirrored between an internal disk and a SAN disk.

A mksysb only captures the contents of rootvg. mksysb is really just another command called savevg on steroids, it (mksysb) is used for creating a bootable image. savevg and restorevg are the commands that you want for saving and restoring non-rootvg volume groups. They in turn invoke a command called backup (/usr/sbin/backup) which essentially creates a big tar file (different format from tar of course and capable of creating files >2GB in size). Corresponding command to "backup" is "restore", which can be used to view contents of a mksysb or savevg file.

A good place to start learning about this stuff is covered in the redbooks returned if you use this link:

www.redbooks.ibm.com/cgi-bin/searchsite.cgi?query=AIX+administration

The redbooks that show up may seem rather dated but the most basic functions that AIX LVM provides have not really changed since those books were written, at least not from a sysadmin perspective. Nowadays you can have resizable volume groups and can reduce filesystems in size and a few other things not covered by those books, but getting a grip on the concepts presented and being able to perform operations found in those mauals is a good place to start.

Hope this helps >< bOOtnix
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