[PATCH qemu-server 1/2] blockdev: add set write threshold
Tiago Sousa
joao.sousa at eurotux.com
Sat Aug 2 18:42:39 CEST 2025
Signed-off-by: Tiago Sousa <joao.sousa at eurotux.com>
---
src/PVE/QemuServer/Blockdev.pm | 52 ++++++++++++++++++++++++++++++++++
1 file changed, 52 insertions(+)
diff --git a/src/PVE/QemuServer/Blockdev.pm b/src/PVE/QemuServer/Blockdev.pm
index 0cc4a0f6..a5d7a3b9 100644
--- a/src/PVE/QemuServer/Blockdev.pm
+++ b/src/PVE/QemuServer/Blockdev.pm
@@ -567,9 +567,61 @@ sub attach {
die $err;
}
+ set_write_threshold($storecfg, $vmid, $drive, $options);
+
return $blockdev->{'node-name'};
}
+sub block_set_write_threshold {
+ my ($vmid, $nodename, $threshold) = @_;
+
+ print "set threshold $nodename $threshold\n";
+
+ PVE::QemuServer::mon_cmd(
+ $vmid,
+ "block-set-write-threshold",
+ 'node-name' => $nodename,
+ 'write-threshold' => int($threshold),
+ );
+}
+
+sub compute_write_threshold {
+ my ($scfg, $volid) = @_;
+ my $lv_size = PVE::Storage::volume_size_info($scfg, $volid, 5);
+
+ # FIX: change these vars to config inputs
+ my $chunksize = 1024 * 1024 * 1024; # 1 GB
+ my $alert_chunk_percentage = 0.5; # alert when percetage of chunk used
+
+ my $write_threshold = $lv_size - $chunksize * (1 - $alert_chunk_percentage);
+
+ return $write_threshold;
+}
+
+sub set_write_threshold {
+ my ($storecfg, $vmid, $drive, $options) = @_;
+
+ my $volid = $drive->{'file'};
+ my ($storeid) = PVE::Storage::parse_volume_id($volid);
+ my $support_qemu_snapshots = PVE::Storage::volume_qemu_snapshot_method($storecfg, $volid);
+ my $scfg = PVE::Storage::storage_config($storecfg, $storeid);
+
+ # set write threshold is only supported for lvm storage using
+ # qcow2+external snapshots
+ return if $scfg->{type} ne 'lvm' || $support_qemu_snapshots ne 'mixed';
+
+ my $snapshots = PVE::Storage::volume_snapshot_info($storecfg, $volid);
+ my $parentid = $snapshots->{'current'}->{parent};
+ # for now only set write_threshold for volumes that have snapshots
+ if ($parentid) {
+ my $drive_id = PVE::QemuServer::Drive::get_drive_id($drive);
+ my $nodename = get_node_name('file', $drive_id, $drive->{file}, $options);
+ my $write_threshold = compute_write_threshold($scfg, $volid);
+
+ block_set_write_threshold($vmid, $nodename, $write_threshold);
+ }
+}
+
=pod
=head3 detach
--
2.39.5
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