Re: lvm + loopback

[Bali Zaci <zaci.bali@gmail.com>]

Ok,

So the problem was that the losetup doesn't able to handle the 'm' char...

So the right command:

losetup -f -v -o $((47105 * 1024 * 1024)) /dev/sda2

Regards,

B

2012. március 31. 18:56 Bali Zaci írta, <zaci.bali@gmail.com>:

Hi all,

I have the following setup: pv (/dev/sda2) -> vg (name: vg) -> lv (name: test)

I would like to create a loopback device on /dev/sda2 (using offset) so the loopback will be exactly the test logical volume.

It is working with a testfile but somehow It is not working with a "real device".

So the steps are the following:

1., Clean the lv and create a pattern that I should find at the begin of the loopback device

# dd if=/dev/zero of=/dev/mapper/vg-test

# echo 'AAAA' > /dev/mapper/vg-test

# sync

# hexdump -C -n 10 /dev/mapper/vg-test 

00000000  41 41 41 41 0a 00 00 00  00 00                    |AAAA......|

0000000a

2., Check the PE size (4M)

# pvdisplay |grep 'PE Size'

  PE Size               4.00 MiB

3., Check where is the first PE on the partition (1M)

# pvs -o +pe_start

  PV         VG   Fmt  Attr PSize   PFree 1st PE 

  /dev/sda2  vg   lvm2 a--  465.56g    0    1.00m

4., Check where the lv is located on the pv (starting at the 11776 PE)

# lvdisplay -m vg/test

  --- Logical volume ---

  LV Name                /dev/vg/test

  VG Name                vg

  LV UUID                vT5X5z-1CJH-uw4n-Jcs8-DW50-PDDB-N6PlIu

  LV Write Access        read/write

  LV Status              available

  # open                 0

  LV Size                419.56 GiB

  Current LE             107408

  Segments               1

  Allocation             inherit

  Read ahead sectors     auto

  - currently set to     256

  Block device           253:4

   

  --- Segments ---

  Logical extent 0 to 107407:

    Type linear

    Physical volume /dev/sda2

    Physical extents 11776 to 119183

5., Create a loopback device on /dev/sda2 (pv) with offset based on the following calculation: Where is the first PE on the device (1M) + Where is the firt PE of the test lv (11776)*PE size (4M) = 47105M

# losetup -f -v -o 47105m /dev/sda2

Loop device is /dev/loop0

6., Test it with hexdump (it should give the same result like in the firts step but id doesn't do it)

# hexdump -C -n 10 /dev/loop0

00000000  00 00 00 00 00 00 00 00  00 00                    |..........|

0000000a

Could somebody give me a hint where is the problem?

Thanks and regards,

B

_______________________________________________
linux-lvm mailing list
linux-lvm@redhat.com
https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/