hi all,

i have little misunderstanding here and it will be great if someone can point me out. I am dealing with this LVM thingy and come across to this pvcreate,vgcreate, and lvcreate. Somehow, before we could create those partition, the disk should be in linux or linux lvm system.

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[root@XXXXXXX /]# fdisk -l

Disk /dev/sda: 6442 MB, 6442450944 bytes
255 heads, 63 sectors/track, 783 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sda1 * 1 13 104391 83 Linux
/dev/sda2 14 783 6185025 8e Linux LVM

Disk /dev/sdb: 2147 MB, 2147483648 bytes
255 heads, 63 sectors/track, 261 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sdb1 1 261 2096451 83 extended

Disk /dev/sdc: 2147 MB, 2147483648 bytes
255 heads, 63 sectors/track, 261 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System

Disk /dev/sdd: 2147 MB, 2147483648 bytes
255 heads, 63 sectors/track, 261 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/sdd doesn't contain a valid partition table

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Let say now i will partition it... and i reach a step :

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Command (m for help): n
Command action
e extended
p primary partition (1-4)
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Q1. What the different between extended and primary partition?
Q2. If i use extended, i cant format it as "linux lvm" or "linux" system. Why?
Q3. From Q2, is it because it was another HDD so it should formatted as primary first then only i could use "extended" space for this partition?

Please clarify abit for me. I think i miss a little bit here. Thanks.

Theoretically, if you use LVM , u should get Linux LVM partition, but in practice i don't see much differences between the two.

Q1. They are the same actually. If you only uses primary partition , you are limited to 4 partitions on the physical disk. The extended partition leverages this whereby you can expand the number of partitions to about 15 partitions (inclusive of the primary). Alternative to fdisk is "parted", which i prefer the latter. You have to download parted though.

Q2. Because you only format the physical disk and not the partition on the disk. Before you use extended, you need to configure it as primary first. You may want to use parted for this.

Q3. I think my answer in 2 answers this one

Thanks bro, i get u now.... simply say, by partitioning/format HDD using fdisk and LVM partition are two different thing?

parted? can elaborate abit more?

the biggest advantage of using LVM is you can expand or shrank your partition size. To have a better picture how LVM work, kindly refer to this link http://www.redhat.com/docs/manuals/enterpr...-lvm-intro.html

the differences between primary and extended:
- you can have max 4 primary partitions
- max 1 extended partition.

you can have 3P+1E (3 Primary + 1 Extended)

sorry for another problem i encounter now.... i have create the pv, vg, and lv. Successfully mounted and edited /etc/fstab.
I try reboot for the first time. All fine ! can access the mount point. Then when i reboot for the second time, the error came out cant find one of the lv i created and mounted. The booting process stuck there and ask me to login for filesystem repair.

Q1. What should i do to troubleshoot it now?
Q2. It say cant find the /dev/vlg/XXX. XXX is the lv i created and mounted on /test2. So basically i assuming something wrong the partition. When i trying to access the /etc/fstab, it say only in read-only mode. I cant edit. So i cant remove the mount entry i put inside. Any help on this? Thanks thanks thanks in advance!

hmm strange, 3nd reboot then failed? and how come u not able to write /etc/fstab??
how u configure LVM, can put ur steps here..

Q2:
Can u open and view the fstab file... if can then just use vi toedit and force save it... force save command q!

I done it right. All the step was 100% confirmed correct since i followed a book step by step.
I think i found the root cause. 1 of the physical volume corrupted. I mean the HDD "died". So when the /etc/fstab boot up trying to search for /dev/vlg/xxx, the error say couldn't find. Now my only problem is tht cant edit the /etc/fstab file. I tried to force edit it also cannot. It keep say the file only in read-only mode.

Q1. How could i reset the setting i done since i am not allowed to tell the kernel tht the /dev/vlg/xxx no longer exist?

Basically you are in emergency mode where the filesystem is mounted read-only.
You can fix this easily with the command:

This will remount the root '/' filesystem to read/write.

I'd also like to add that LVM does need to use a partition If you are using the entire disk as a PV, you can simple make the raw unpartitioned disk as PV, something like:


You only need to make LinuxLVM partitions if you are not using the whole disk for LVM. (such as on your /dev/sda)

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Added on July 1, 2009, 8:36 pmI'd like to help clarify your initial question about partitions. Apologies upfront for the length.

When the msdos partition table was first invented, it only allowed the creation of 4 partitions.
These became known now as Primary partitions. (You can have only 4)

Later on, to overcome this limitation, a new type of partition called an Extended partition was invented. This was not an actual partition but is actually just a container designed to extend the limitation of the msdos partition table & allow for many more (logical) partitions.

You can have only 1 Extended partition & it must take the place of 1 of the Primary partitions.It should also take up all the free space on the disk. (This is because Logical partitions will be created inside the Extended partition container)

So a typical disk layout on Linux would look like this:
Total Cylinders on Disk = 4866
/dev/sda1 - Primary - Cylinder 1-398 - Linux Swap
/dev/sda2 - Primary - Cylinder 399-1021 - Mounted on /
/dev/sda3 - Primary - Cylinder 1022-2083 - Mounted on /home
/dev/sda4 - Extended - Cylinder 2084-4866 - Extended Container
/dev/sda5 - Logical - Cylinder 2084-3142 - Mounted on /usr
/dev/sda6 - Logical - Cylinder 3143-4866 - Mounted on /var

Notice that the Cylinder start for sda4 & sda5 is the same, this is because sda5 & sda6 are logical partitions that can only exist inside the Extended partition container.

In Linux, logical partitions always start from 5, the numbers 1-4 are reserved for the 4 Primary partitions (including the 1 Extended).

This post has been edited by ongte: Jul 1 2009, 08:36 PM

Bro, ur info help me alot!! Many thanks!!!!

Yup, you got the idea dude!



parted (under GNU license, i think) is another partition manager similar to fdisk. It's just a matter of preference though, but i find parted easier to use compared to fdisk.

For the problem you encountered after booting where you lose the LV, I believe you may have missed one or two final steps to write the changes to the disk when using fdisk.

I think he means gparted or qtparted. I think gparted is better. Its in the repo's.
BTW, extended partition can be anywhere, not the last one. Also swap need not be in primary, can be in one of logical in extended. Windows, at least XP needs to be 1st partition. FreeBSD, open BSD etc needs to be in primary, if installed to one of logical in extended, it will wipe out the other logical partitions.