[PVE-User] Guest LVM2 overhead/usefulness for thin storages (Ceph, ZFS)

[Marco Gaiarin]

A collegue here came from the old school of 'LVM everything', that
surely make sense for 'phisical servers'.

Also, point me that make sense also for some 'virtual servers' (or
better, 'virtual storage') setup.
EG, considering a SAN, splitting virtual volumes in predefined chunks
(1/2TB) and 'recombine' them via LVM in the guest, permit to move
around smaller volumes, transparently for the guest.


But if we came to 'modern', thin storage, like ZFS or Ceph, this still
make sense?
Seems 'no' to me, seems to me only useful to add another layer of
abstraction... and the same functionality can be achived splitting data
in virtual disks as if was volumes, format with a single partition per
disk, and eventually extend the disk...

And, this layer, how does it 'cost'? Not only in the term of
performance, but also functionality... eg, 'trim' can traverse correctly
all the layers?


I hope i was clear. Thanks.


PS: i've tried to look at the wiki but found nothing; if i've missed
    something, point me to the doc!

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