[linux-lvm] lvm over loop device

[geert Geurts]

hello steve,
Thanks for your reply, It seems logical not to have a extent larger than the
phisical size...
i don't have time right now but I'll look into it next week.
Thanks,

Greetings,
Geert

2008/9/30 Steve Brueggeman <xioborg at yahoo.com>

> I didn't see any replies to this, so I thought I'd post what I've found.
>
> You have to specify a smaller extent size when creating the volume group.
>  The
> default extent size is 4MB, which is larger than your physical device on
> /dev/loop1 (use the -s option)
>
> For example, try this instead, which would give 4 extents on the 1MB
> physical
> device on /dev/loop1 (I think.  I am not certain about how much metadata
> exists
> on the physical device for LVM2)
>
> >vgcreate SmallDiskGroup -s256k /dev/loop0 # create a new volumegroup using
> the
> >loop0 device as phisical volume.
>
> Steve.
>
>
> On Mon, 29 Sep 2008 11:44:40 +0200, you wrote:
>
> >Hello Bryn,
> >I haven't had the time yet to try Stuart's suggestion... I've re did my
> >attempt to create the lv though, and this time with the -vvv option in
> >the step where I create the lv.
> >my steps:
> >dd if=/dev/sdb1 of=./disk0 # copy a existing LVM-partition to a file
> >losetup -f ./disk0        # link the file to a loop device
> >pvcreate /dev/loop0       # create a pv using the file
> >vgcreate SmallDiskGroup /dev/loop0 # create a new volumegroup using the
> >loop0 device as phisical volume.
> >vgchange -a y SmallDiskGroup #Activate the volumegroup
> >
> >nb. vgdisplay SmallDiskGroup gives 'Act PV 1' but 'MAX LV 0'
> >
> >the output of lvcreate -vvv -L1 -nSmallDiskVolume SmallDiskGroup is
> >downloadable here: http://pastebin.com/pastebin.php?dl=m2b9dcd7f
> >
> >I hope you can find anything.
> >
> >Greetings,
> >Geert
> >
> >On Mon, 2008-09-29 at 10:08 +0100, Bryn M. Reeves wrote:
> >> -----BEGIN PGP SIGNED MESSAGE-----
> >> Hash: SHA1
> >>
> >> geert Geurts wrote:
> >> > So what I did first create a LVM partition of 1MB on a memorystick and
> then
> >> > change the if of dd to point to the LVM partition, I'm now able to
> pvcreate
> >> > /dev/loop0, vgcreate SmallDisk /dev/loop0.
> >> > But I'm unable to create a logical volume in the SmallDisk group...
> >> > what am I doing wrong here? is it even possible if not why?
> >>
> >> Hi Geert,
> >>
> >> What was the error you were getting at this point? If possible, can you
> >> use a service like pastebin.com to post the complete output of
> "lvcreate
> >> - -vvv" with the options you're using for the SmallDisk VG. That should
> >> give enough detail to have some idea where it's failing.
> >>
> >> I think the idea is reasonable enough although you'll probably need to
> >> do some fiddling around to get the size/number of the gmailfs volumes
> >> right to give good performance.
> >>
> >> Snapshots could definitely work here but I think it might be a bit
> >> tricky without some of the patches that are currently outstanding for
> >> device-mapper, esp. Mikulas' snapshot merging patches which you'd need
> >> to "restore" one of the COW areas. See the thread here:
> >>
> >> http://kerneltrap.org/Linux/LVM_Snapshot_Merging
> >>
> >> Regards,
> >> Bryn.
> >>
> >> -----BEGIN PGP SIGNATURE-----
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> >> Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org
> >>
> >> iEYEARECAAYFAkjgmxgACgkQ6YSQoMYUY96LegCcCHPZNLfhTUjIrsLiJcgROTDV
> >> +SwAoLFQDiGpkZl5tpEFW5hjFH+6OuAj
> >> =i+W8
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> >>
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> >> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
> >
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>
>
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