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

Yanni M. gianni.milo22 at gmail.com
Wed Jun 30 15:40:06 CEST 2021


Personally I favor the flexibility that LVM offers when it comes to
creating/resizing volumes (growing/shrinking), most of times without even
needing to reboot the vm. Even if it's possible to do the same with disk
partitioning, it's not as trivial as with lvm (hence why it was invented in
the first place). Having to create a new vdisk on the host for each
individual volume that you might need for the guest in the future - even
though possible - it does not look as clean solution as doing all these,
with lvm, within the guest. The overhead of the lvm is minimal and the
discard/trim should be already enabled by default. Special care should be
taken when using ThinLVM to avoid situations where the pools get full etc
(same apply when used at the host level). Apart from that, it does not
require any special administration skills, apart from familiarity with lvm
tools obviously. To be clear, I'm not defending lvm in here. Both your and
this method are ok. It's all about with what each person is familiar with
and how each organise their work.

On Wed, 30 Jun 2021 at 10:29, Marco Gaiarin <gaio at sv.lnf.it> wrote:

>
> 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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