ProxmoxVE patch for Ceph RBD tuning.Taken from https://pve.proxmox.com/pipermail/pve-devel/2018-June/032787.html with debugging output

QemuServer.pm.diff

diff -u /usr/share/perl5/PVE/QemuServer.pm*
--- /usr/share/perl5/PVE/QemuServer.pm0	2019-05-25 12:40:24.000000000 +0300
+++ /usr/share/perl5/PVE/QemuServer.pm	2019-06-24 07:06:34.825186937 +0300
@@ -1881,6 +1881,18 @@
 	$device .= ",serial=$serial";
     }
 
+    my $volid = $drive->{file};
+    if ($volid && $drive->{discard}) {
+        my $storage_name = PVE::Storage::parse_volume_id($volid);
+        if ($storecfg->{ids}->{$storage_name}->{type} eq 'rbd') {
+            $device .= ",discard_granularity=4194304";
+            print "DBUG: VM $vmid, volume $volid = rbd, discard\n";
+        } else {
+            print "DBUG: VM $vmid, volume $volid = no rbd\n";
+        }
+    } else {
+        print "DBUG: VM $vmid, volume $volid = no discard\n";
+    }
 
     return $device;
 }