[pve-devel] Change the form in that the DRBD resource are created in PVE GUI

[Cesar Peschiera]

Hi PVE developers team

Please, let me to do a suggestion (this topic is a bit complicated):

I suggest that in PVE 4.x, in the use of the PVE GUI, LVM is on top of DRBD
(instead of DRBD in top of LVM), of this mode, each LV (logical volume) can
to have the same size of the virtual hard disk.

Why is good idea this concept?:

In the current state, each DRBD resource have all size of a partition or a
hard disk. Then, as in the datacenter is need run several scheduled tasks,
as:

a) The backups of our VMs, that minimally should be done every day (until
now without options of incremental or differential).
b) The verification of all DRBD resources (at least once by week if the
information is critical).
c) The hardware verification of blocks of disk in the RAIDs created (at
least once by week if the information is critical, besides, the RAIDs
controllers as LSI , Adaptec, etc. has this options, and his manufacturers
recommend their use periodically).

And as all these tasks require much time, i think that the PVE GUI for the
creation of DRBD resources must be modified, ie, that each DRBD resource has
the same size of the virtual disk, of this mode, the verification of all
DRBD resources will take much less time to complete.

Disadvantage of this request:

If LVM is on top of DRBD, will be impossible to do a resize of virtual disk
in hot because the LV (logical volume. ie, the virtual disk) must be
previously unmounted, as also, obviously,  previously the virtual machine
should be turned off, only of this mode the DRBD resource can be resized.

Talking within of this context and using DRBD 8.x, I have tested many times 
all these tasks in production environments with PVE 3.x., and always 
successfully.

And please, also be aware that the verification of DRBD resources must be
made periodically (in shorts times of wait between a and other
verification), while that the need of do a resize of a virtual disk is only
sporadic.

In summary:

If "drbdmanage" can't change the size of a DRBD resource in hot, i think
that the PVE GUI may do it, but also not in hot, and will need to have
previously turned off the VM and unmounted the LV (logical volume, ie, the
virtual disk, and maybe in both PVE nodes) for do the resize of DRBD
resource, and afterward it may resize the LV (accordingly, the size of the
virtual disk).

Question:
Will be possible to make such change?

Best regards
Cesar