Dne 13.7.2017 v 15:25 Matthias Leopold napsal(a):
hi,
i'm fiddling around with LVM backed KVM raw disks, that i want to use
_directly_ in oVirt virtualization (as "Direct LUN"). i would like to avoid
"importing", dd, etc. if possible. in the KVM origin system exists a mapping
of one iSCSI whole device (no partitions) to one PV to one VG to one LV per
KVM disk. i can now present these iSCSI devices to the oVirt hosts, where i
can only use them as "Direct LUN" without the LVM layer (i guess). so all i
would need is to remove the LVM metadata from the iSCSI device preserving the
"content" of the LV. pvremove seems to be too "intrusive" for this... i know
this sounds rather naive and i didn't find any recipes for it. everybody talks
about dd to a new device, which of course works (i tried it), but is exactly
what i want to avoid when migrating very large disks (TB). i hope someone
understands my concern and maybe has a solution
Hi
Yep, it really sounds a bit naive :)
PV has 'header' so the real 'data' are shifted by PV header+lvm2 metadata.
and also LV does not need to be sequential.
However if you have been having a single 'segment' LV and and you calculate
proper skipping offset (typically 1MB) you can try to use such device directly
without lvm2 with a loop device mapping - see losetup --offset option - but
you would need to use this everytime you want to access such storage - so
there is not a single magic 'flip' which would make an LV to appear like
regular device.
Regards
Zdenek
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