AIX Logical Volume Manager Introduction

                                                                           AIX Logical Volume Manager (LVM)

The AIX LVM components are PV, LV, PP, LP and VG. Considering the maximum limitation of PVs , LVs ,PPs and size of physical partition the volume group types has been defined such that normal , big and scalable volume group. Volume Group Descriptor Area, Volume group status Area and Logical Volume Control Block (LVCB) plays a vital role in AIX logical volume manager which is unique from other operation systems LVM and it holds the Meta data information about volume group.

Volume Group Descriptor Area (VGDA) :-
Volume Group Descriptor Area (VGDA) which keeps the track of which physical volume belongs to which volume group and proprieties of the physical volume. As per the logical volume manager architecture it is mandate that every physical volume must have at least one VGDA and the VGDA information is same for the entire disk are part of the particular volume group. Moreover, VGDA architecture and internals varies depending upon the volume group type.

VGDA Major Role :-
The VGDA plays the major role for the quorum voting , which used to give the status for the disk missing / removed and etc … VGDA has been divided in to three major parts those are volume group header , list of logical volume entries and physical volume entries.
We can check the number VGDA in a particular disk through lspv.

Volume Group Status Area (VGSA) :-
Volume group status Area (VGSA), which keeps the track of the physical partition status of all the physical volumes, belongs to the same volume group. VGSA ensures the stale and synchronization information about physical partition. Each and every read or write request being served by the LVM device driver , if the device driver doesn’t read/write then VGSA makes the partition status as stale , once the particular partition became available than VGSA re-synchronize will be initiated and it ensures that the physical partition status to up to date. Basically VGSA location depends on the bit map and volume group type.

Logical Volume Control Block (LVCB) :- 
Logical Volume Control Block (LVCB) has the details about logical volume details such that number of logical partition and allocation policy. Methodology of keeping LVCB varies depends upon the volume group. Even if the LVCB corrupt also the logical volume would be stable and usable too. If Logical Volume Control Block is not updated means we will get the message such that ” Warning, cannot write lv control block data ” . Important this is that LVCB is not required for many of the LVM operations.

LVCB Command :- 
getlvcb -AT lvname is the command will show the details about LVCB.

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