[pve-devel] Implement "resize" for the DRBD backend.

[Cesar Peschiera]

>> > -    #my $cmd = ['/sbin/lvextend', '-L', $size, $path];
>> > -    #run_command($cmd, errmsg => "error resizing volume '$path'");
>> > +    # FIXME if there's ever more than one volume in a resource
>> >
>> > not sure if we ever want to support multiple volumes inside one
>> > resource?
>> > Why would we want to do that?
>> So that the volumes use a common write stream across the network.
>>
>> If you have eg. a database that uses 3 volumes (data, log data,
>> write-ahead
>> log), you want to have these three at the *same* point in time.
>>
>> When one of 3 connections breaks, then the other two volumes could run
>> ahead - and if the Primary node breaks down at that time, the Secondary
>> wouldn't have 3 consistent volumes, which might lead to troubles.
>
> Ah, OK.

Hi Dietmar
I am agree with Philipp Marek, but such setup has his disadvantages...

For example, i have a VM with 4 volumes in different arrays of disks
(properly installed with SAS 15K 600GB. and several RAID-10 and a RAID-1),
also i have several NICs 10Gb/s connected in mode NIC-to-NIC with
bonding-rr, and finally, to crontab i have added a script that do a
verification of all replicated DRBD volumes, and it is executed once for
week.

Then, with this setup, if i have a DRBD resource for each volume, i can do
the verification of the 4 volumes simultaneously, otherwise, ie if i have a
DRBD resource for several volumes, DRBD can not do the verification
simultaneously for each volume, and this task will take a long time for
finish.

Moreover, as i have several NICs for my DRBD resources, i have the advantage
of use a total higher bandwidth for these simultaneous verifications (the
sum of bandwidth available of each NIC). Ie, that if i have several volumes
in a only DRBD resource, i can not take advantage of a total higher
bandwidth using the others NICs available.

Moreover, with DRBD, in dual primary mode, it is very easy resynchronize the
resources online, ie, without turn off nothing, and if i have each DRBD
resource separated in NICs, while that the resynchronize is in progress, it
will finish in less time.

Moreover, how much is the possibility that a hard disk, or one DRBD resource 
breaks down, and simultaneously or in a short time, a Server ???

Finally, and if is possible, i would like to have the option of configure 
only a volume for each DRBD resource for each VM.

Best regards
Cesar