Re: Debian in a VMware VM and LVM

On Tuesday 13 March 2012 22:52:01 Bonno Bloksma wrote:

Using the 6.0.4 amd netinst CD I created a small 10GB virtual machine (VM).
I then realized I needed it to be a bit bigger so I wanted to extend the
LVM environment and add that space to the /var logical volume. Of course
as this is a new VM I just could have started from scratch but I am trying
to learn something as well. ;-)

First I had a look at the current disk layout using fdisk -l

root@wwwgw:~# fdisk -l

Disk /dev/sda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000d6e97

Device Boot Start End Blocks Id System
/dev/sda1 1 37 291840 83 Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2 37 1306 10190849 5 Extended
/dev/sda5 37 1306 10190848 8e Linux LVM

1)
Why the warning about the 300MB /boot partition not ending on a cylinder
boundary? I used the manual setup in the Debian 6.0.4 installation and
told it to create a 300MB partition at the beginning of the disk. Did the
installation software do something wrong or should I have know something I
do not know yet?
Older versions of fdisk by default aligns to cylinder. This is deprecated and
not the case now. Simply suppress this warning by using -cu

2)
After that came a lot of warnings about /dev/dm-0, /dev/dm-1, /dev/dm-2,
/dev/dm-3 and /dev/dm-4. I know those are LVM2 devices but... Why is fdisk
(still) seeing them as disks/partitions it has to show during a listing,
and then complain they are not valid?

I think this is a bug in fdisk.

At the VMware level I increased the disk from 10GB to 12GB. Using cfdisk,
which in my opinion gives less cause for a user error, I created a new
logical sda6 partition in the free space. The end result is: root@wwwgw:~#
fdisk -l

Disk /dev/sda: 12.9 GB, 12884901888 bytes
255 heads, 63 sectors/track, 1566 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000d6e97

Device Boot Start End Blocks Id System
/dev/sda1 1 37 291840 83 Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2 37 1566 12285008 5 Extended
/dev/sda5 37 1306 10190848 8e Linux LVM
/dev/sda6 1306 1566 2094127+ 8e Linux

3)
Why is there a + at the end of the number of blocks?
In fdisk, a block is 1024 bytes. The partition does not contain integral
number of blocks, hence the + sign.

I then want to make the sda6 partition a LVM physical volume using
root@wwwgw:~# pvcreate /dev/sda6
Device /dev/sda6 not found (or ignored by filtering).
root@wwwgw:~#
indeed, there is no /dev/sda6 yet.

4)
Why is /dev/sda6 not there yet? What step am I missing?
You should run partprobe(8) or reboot your machine.


Ok, after a reboot (it is not a production server yet) the /dev/sda6 is
there. Form here on it was (almost) straight sailing. ;-)

root@wwwgw:~# pvcreate /dev/sda6
Physical volume "/dev/sda6" successfully created
root@wwwgw:~# vgextend vgroup1 /dev/sda6
Volume group "vgroup1" successfully extended

Then to runlevel 1 to make sure (almost) nothing is using the /var
directory tree and
root@wwwgw:~# lvextend -l+2G /dev/vgroup1/lvvar
Extending logical volume lvvar to 3.86GiB
Logical volume lvvar successfully resized

root@wwwgw:~# umount /var
Then first a filesystem check as that seems to be needed before resizing.
Not doing so will give me a warning although this was not mentioned in the
HOWTOs I have read. root@wwwgw:~# fsck -f /dev/vgroup1/lvvar
root@wwwgw:~# resize2fs /dev/vgroup1/lvvar
root@wwwgw:~# mount /var

and back to runlevel 2


Anything else I missed?

Bonno Bloksma


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