question about LVM

[fishjuli]

Logical volume name can replace a disk device in all normal operating system commands, True or Flase?

[Tim Adamson_1]

false

[Tim Adamson_1]

Can you describe what you are trying to do?

I'm sure you will be provided the commands to help you achieve the task at hand.


Tim

[fishjuli]

Thanks for reply.
This is a lab from the MirrorDisk(H6285S) to check the understanding of LVM. I have no idea of the question.

[fishjuli]

BTW, the answer is True. Could anybody give an explanation for it?
Thanks.

[Artyom Voronchihin]

Right answer is TRUE ! See solutions at the end of the Student Workbook.

[Sridhar Bhaskarla]

Hi,

In a way, I don't like the way the questions are formulated in those exams. Most of them look so ambiguous that the answer may not reveal the user's skillset.

I believe they were asking if a LV can be used as a substitution for disk under normal operations which is true. Unless I hear a different explanation of this question.

-Sri

PS: This forum is intended to help people that are in real need. Not to get answers for certification exams.

[Tim Adamson_1]

What is the context of the question?

If you want to dd a disk, and the lvol only spans part of the disk, if you dd the disk device you will dd the whole disk. You can dd the lvol but will only dd part of the disk.


Tim

[Massimo Bianchi]

Hi,
i didn't attented that course, but the answer in HPUX is true.


LVM is the replacement for the managing of the disks and disk space, and it takes care of everything.

After the disks are initialized (pvcreate) and some boot stuff is placed (mkboot) all control is passed to lvm.

FS creation, snpashots, mirroring, all occurs at lvm level.

You create a FS on a logical volume, insted on a phisical disk.

I suggest you to have a look at "man lvm", almost all is there. I started there :)

Massimo

[fishjuli]

Could you tell me the reason?

[James Murtagh · Accepted solution]

Hi,

Well from my point of view, taking the question literally the answer is false. Can the lvol replace a disk in the diskinfo command for example? That obviously is not how the question was intended, hence I agree with Sri's point - this is totally ambiguous.

The only thing I can think of is before lvm you used to partition disks using the sector convention, i.e. /dev/dsk/c0t0d0s0 which would be replaced by /dev/vgXX/lvol1 in lvm. In this case lvm does take over.

I would complain at the exam if I was given that with no context!

Cheers,

James.

[Massimo Bianchi]

Because it's more efficent.

back to hard sectioned disks, a FS can reside only on 1 disk, at most.

So, if you have a 2G disks, your bigger FS can be of 2G.

With LVM, you group the space togheter, in a VG (volume group) and use it at your needs.


Let's suppone that you have 5 disks of 2G.

You can decide to create 1 logical volume of 10G, or 1 logical volume of 4 G and a 2G logical volume with 2 mirror copies for reduncancy, or you can create 1 Gb logical volume, and take the remaining space free for future needs.


With OnlineJFS you can even increase the FS size online, without rebooting in single single user/maintenance mode.


You can mix the space from many different storage.


Substantially, lvm gives you the power of elevating from the phisical layer and think only at the space, without taking care of phisical layout and limitations.

Massimo

[fishjuli]

thanks all for your reply.

[fishjuli]

James, I agree with you.

[Dave Wherry]

Sri,
Regarding your P.S., I'm not sure I see a problem with this question being posted here. The forum is not meant to be a replacement for the Response Center, for a person in need. There was a question and several people stepped up to answer it. That's what the forum is about.
Points were also assigned. Can it get better than this?