[linux-lvm] lvm + loopback
Bali Zaci
zaci.bali at gmail.com
Sat Mar 31 19:47:56 UTC 2012
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 at 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
>
>
>
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