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

[Eneko Lacunza]

We continue to use LVM in VMs too. It adds flexibility in how you add 
additional storage to the VM (you could add a second disk from a 
different storage for example, an merge to root LV or whatever).

Also, extending partitions after growing disk is only possible on last 
partition, and it has been a bit tricky to do so until recently on some 
distros.

So can you avoid needing to use it? Sure.

Could you make use of it in some situations? Yes, of course.


El 30/6/21 a las 15:40, Yanni M. escribió:
> 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!
>>
>> --
>> dott. Marco Gaiarin                                     GNUPG Key ID:
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>>
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Eneko Lacunza
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