An error about VGDA in the storage management chapter of IBM_AIX training PPT

A few days ago, I went down an AIX Chinese Version training PPT, which corresponds to the IBM official document AIX 5L System Administration I: Implementation Studemt Notebook. I have read several English documents and have a biased understanding of some basic concepts in Chinese. Therefore, I have read this PPT and I think it is quite rewarding to explain it well.

But when I saw the VGDA volume group description area yesterday, I was puzzled. I would like to popularize the knowledge of VDGA first.

Volume Group description Area: VGDA (Volume Group Descriptor Area)

VGDA is an area on a hard disk that contains information about the entire volume group, such as all logical and physical volumes owned by VG.

When a PV is added or deleted in a VG, the information in VGDA is modified accordingly.

To ensure the integrity of logical and physical volume management data in the volume group, to activate a volume group, the system requires that there be sufficient number of available VGDA, that is, to meet the requirements of quorum

Quorum generally requires at least 51% availability.

The following is a questionable PPT:

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Figure 1 VGDA distribution chart

The following two explanations in the second figure are understandable. When I saw the third figure, the following sentence puzzled me for a long time: "If any PV breaks down, 66% VGDA is available ", if PV1 breaks down, the remaining 2/4 is available. The reason should be 50%. If PV2 and PV3 break down, the remaining 3/4 is available, that is, 75% of VGDA is available. Why can't it reach 66%.

I thought it was possible that the document was wrong. Later I consulted a master who found the information for me so that I was sure that the PPT was wrong. Please read the truth.

650) this. width = 650; "src =" http://www.bkjia.com/uploads/allimg/131227/1P54SD6-1.jpg "title =" VGDA2.jpg "/>

Figure 2 Disk Quota

It's different. In the original figure PV1, a vgda is added, and the calculation result is different.

Thanks to the expert for his help. The accuracy of his information is worth learning. If we question something, we should try to seek evidence to prove whether it is right or wrong.

This article is from the "cabbage" blog, please be sure to keep this source http://zhengyongkun.blog.51cto.com/1163218/1218688