I started playing around with this today (finally ;))
but immediately ran into an issue..
VM is running, LVM storage configured, adding a new 32G disk to the VM with
format=qcow2:
update VM 106: -scsi1 extsnap:32,format=qcow2,discard=on,ssd=on,iothread=on
qcow2 overhead: 4096
LV size: 33558528
Logical volume "vm-106-disk-0.qcow2" created.
Formatting '/dev/extsnap/vm-106-disk-0.qcow2', fmt=qcow2 cluster_size=65536
extended_l2=off preallocation=metadata compression_type=zlib size=34359738368
lazy_refcounts=off refcount_bits=16
qemu-img: Failed to flush the refcount block cache: No space left on device
Logical volume "vm-106-disk-0.qcow2" successfully removed.
TASK ERROR: unable to create image: qemu-img: /dev/extsnap/vm-106-disk-0.qcow2:
Could not resize image: Allocating clusters failed: No space left on device
the overhead and LV size messages I patched in for debugging purposes..
something with the overhead calculation must be wrong? if I make the overhead
twice as much, it works..
also see comments below..
> Alexandre Derumier via pve-devel <pve-devel@lists.proxmox.com> hat am
> 22.04.2025 13:51 CEST geschrieben:
> we format lvm logical volume with qcow2 to handle snapshot chain.
>
> like for qcow2 file, when a snapshot is taken, the current lvm volume
> is renamed to snap volname, and a new current lvm volume is created
> with the snap volname as backing file
>
> Signed-off-by: Alexandre Derumier <alexandre.derum...@groupe-cyllene.com>
> ---
> src/PVE/Storage/LVMPlugin.pm | 301 ++++++++++++++++++++++++++++++++---
> 1 file changed, 278 insertions(+), 23 deletions(-)
>
> diff --git a/src/PVE/Storage/LVMPlugin.pm b/src/PVE/Storage/LVMPlugin.pm
> index c4648ec..8ee337a 100644
> --- a/src/PVE/Storage/LVMPlugin.pm
> +++ b/src/PVE/Storage/LVMPlugin.pm
> @@ -4,6 +4,7 @@ use strict;
> use warnings;
>
> use IO::File;
> +use POSIX qw/ceil/;
>
> use PVE::Tools qw(run_command trim);
> use PVE::Storage::Plugin;
> @@ -218,6 +219,7 @@ sub type {
> sub plugindata {
> return {
> content => [ {images => 1, rootdir => 1}, { images => 1 }],
> + format => [ { raw => 1, qcow2 => 1 } , 'raw' ],
> 'sensitive-properties' => {},
> };
> }
> @@ -294,7 +296,10 @@ sub parse_volname {
> PVE::Storage::Plugin::parse_lvm_name($volname);
>
> if ($volname =~ m/^(vm-(\d+)-\S+)$/) {
> - return ('images', $1, $2, undef, undef, undef, 'raw');
> + my $name = $1;
> + my $vmid = $2;
> + my $format = $volname =~ m/\.qcow2$/ ? 'qcow2' : 'raw';
> + return ('images', $name, $vmid, undef, undef, undef, $format);
> }
>
> die "unable to parse lvm volume name '$volname'\n";
> @@ -303,11 +308,13 @@ sub parse_volname {
> sub filesystem_path {
> my ($class, $scfg, $volname, $snapname) = @_;
>
> - die "lvm snapshot is not implemented"if defined($snapname);
> + my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
> + $class->parse_volname($volname);
>
> - my ($vtype, $name, $vmid) = $class->parse_volname($volname);
> + die "snapshot is working with qcow2 format only" if defined($snapname)
> && $format ne 'qcow2';
>
> my $vg = $scfg->{vgname};
> + $name = $class->get_snap_name($volname, $snapname) if $snapname;
>
> my $path = "/dev/$vg/$name";
>
> @@ -335,7 +342,9 @@ sub find_free_diskname {
>
> my $disk_list = [ keys %{$lvs->{$vg}} ];
>
> - return PVE::Storage::Plugin::get_next_vm_diskname($disk_list, $storeid,
> $vmid, undef, $scfg);
> + $add_fmt_suffix = $fmt eq 'qcow2' ? 1 : undef;
> +
> + return PVE::Storage::Plugin::get_next_vm_diskname($disk_list, $storeid,
> $vmid, $fmt, $scfg, $add_fmt_suffix);
> }
>
> sub lvcreate {
> @@ -363,13 +372,43 @@ sub lvrename {
> );
> }
>
> -sub alloc_image {
> - my ($class, $storeid, $scfg, $vmid, $fmt, $name, $size) = @_;
> +my sub lvm_qcow2_format {
> + my ($class, $storeid, $scfg, $name, $fmt, $backing_snap, $size) = @_;
> +
> + return if $fmt ne 'qcow2';
see below - this should be an assert, and it should never be called for
non-qcow2 volumes..
> +
> + $class->activate_volume($storeid, $scfg, $name);
> + my $path = $class->path($scfg, $name, $storeid);
> + my $backing_path = $class->path($scfg, $name, $storeid, $backing_snap)
> if $backing_snap;
> + PVE::Storage::Plugin::qemu_img_create($scfg, 'qcow2', $size, $path,
> $backing_path);
>
> - die "unsupported format '$fmt'" if $fmt ne 'raw';
> +}
> +
> +my sub lvm_size {
> + my ($size, $fmt, $backing_snap) = @_;
> +
> + #add extra space for qcow2 metadatas for initial image
> + #if backing_snap exist, the parent lvm volume already have the overhead
> + return $size if $fmt ne 'qcow2' || $backing_snap;
> +
> + #without sub-allocated clusters : l2_size = disk_size × 8 / cluster_size
> + #with sub-allocated clusters : l2_size = disk_size × 8 / cluster_size
> / 16
> + #ex: 4MB overhead for 1TB with extented l2 clustersize=128k
> + #can't use qemu-img measure, because it's not possible to define options
> like clustersize && extended_l2
> + #verification has been done with : qemu-img create -f qcow2 -o
> extended_l2=on,cluster_size=128k test.img 1G
> +
> + my $qcow2_overhead = ceil($size/1024/1024/1024) * 4096;
> + $size += $qcow2_overhead;
> + return $size;
> +}
> +
> +my sub alloc_lvm_image {
> + my ($class, $storeid, $scfg, $vmid, $fmt, $name, $size, $backing_snap) =
> @_;
> +
> + die "unsupported format '$fmt'" if $fmt !~ m/(raw|qcow2)/;
>
> die "illegal name '$name' - should be 'vm-$vmid-*'\n"
> - if $name && $name !~ m/^vm-$vmid-/;
> + if $name !~ m/^vm-$vmid-/;
>
> my $vgs = lvm_vgs();
>
> @@ -378,17 +417,51 @@ sub alloc_image {
> die "no such volume group '$vg'\n" if !defined ($vgs->{$vg});
>
> my $free = int($vgs->{$vg}->{free});
> + my $lvmsize = lvm_size($size, $fmt, $backing_snap);
>
> die "not enough free space ($free < $size)\n" if $free < $size;
>
> - $name = $class->find_free_diskname($storeid, $scfg, $vmid)
> + my $tags = ["pve-vm-$vmid"];
> + #tags all snapshots volumes with the main volume tag for easier
> activation of the whole group
> + push @$tags, "\@pve-$name" if $fmt eq 'qcow2';
> + lvcreate($vg, $name, $lvmsize, $tags);
> +
> + #format the lvm volume with qcow2 format
and also I just realized that I missed this in my first pass - we should return
here
if the format is not qcow2, instead of making the lvm_qcow2_format a nop in
that case..
> + eval { lvm_qcow2_format($class, $storeid, $scfg, $name, $fmt,
> $backing_snap, $size) };
> + if ($@) {
> + my $err = $@;
> + #no need to safe cleanup as the volume is still empty
> + eval {
> + my $cmd = ['/sbin/lvremove', '-f', "$vg/$name"];
> + run_command($cmd, errmsg => "lvremove '$vg/$name' error");
> + };
> + die $err;
> + }
> +
> +}
> +
> +sub alloc_image {
> + my ($class, $storeid, $scfg, $vmid, $fmt, $name, $size) = @_;
> +
> + $name = $class->find_free_diskname($storeid, $scfg, $vmid, $fmt)
> if !$name;
>
> - lvcreate($vg, $name, $size, ["pve-vm-$vmid"]);
> + alloc_lvm_image($class, $storeid, $scfg, $vmid, $fmt, $name, $size);
>
> return $name;
> }
>
> +sub alloc_snap_image {
> + my ($class, $storeid, $scfg, $volname, $backing_snap) = @_;
> +
> + my $size = $class->volume_size_info($scfg, $storeid, $volname, 5,
> $backing_snap);
> + $size = $size / 1024; #we use kb in lvcreate
> +
> + my ($vmid, $format) = ($class->parse_volname($volname))[2,6];
> +
> + alloc_lvm_image($class, $storeid, $scfg, $vmid, $format, $volname,
> $size, $backing_snap);
> +}
> +
> sub free_image {
> my ($class, $storeid, $scfg, $volname, $isBase) = @_;
>
> @@ -539,6 +612,12 @@ sub activate_volume {
>
> my $lvm_activate_mode = 'ey';
>
> + #activate volume && all snapshots volumes by tag
> + my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
> + $class->parse_volname($volname);
> +
> + $path = "\@pve-$name" if $format eq 'qcow2';
> +
> my $cmd = ['/sbin/lvchange', "-a$lvm_activate_mode", $path];
> run_command($cmd, errmsg => "can't activate LV '$path'");
> $cmd = ['/sbin/lvchange', '--refresh', $path];
> @@ -551,6 +630,10 @@ sub deactivate_volume {
> my $path = $class->path($scfg, $volname, $storeid, $snapname);
> return if ! -b $path;
>
> + my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
> + $class->parse_volname($volname);
> + $path = "\@pve-$name" if $format eq 'qcow2';
> +
> my $cmd = ['/sbin/lvchange', '-aln', $path];
> run_command($cmd, errmsg => "can't deactivate LV '$path'");
> }
> @@ -558,21 +641,31 @@ sub deactivate_volume {
> sub volume_resize {
> my ($class, $scfg, $storeid, $volname, $size, $running) = @_;
>
> - $size = ($size/1024/1024) . "M";
> + my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
> + $class->parse_volname($volname);
> +
> + my $lvmsize = lvm_size($size/1024, $format);
> + $lvmsize = "${lvmsize}k";
>
> my $path = $class->path($scfg, $volname);
> - my $cmd = ['/sbin/lvextend', '-L', $size, $path];
> + my $cmd = ['/sbin/lvextend', '-L', $lvmsize, $path];
>
> $class->cluster_lock_storage($storeid, $scfg->{shared}, undef, sub {
> run_command($cmd, errmsg => "error resizing volume '$path'");
> });
>
> + if(!$running && $format eq 'qcow2') {
> + my $prealloc_opt =
> PVE::Storage::Plugin::preallocation_cmd_option($scfg, $format);
> + my $cmd = ['/usr/bin/qemu-img', 'resize', "--$prealloc_opt", '-f',
> $format, $path , $size];
> + run_command($cmd, timeout => 10);
> + }
> +
> return 1;
> }
>
> sub volume_size_info {
> - my ($class, $scfg, $storeid, $volname, $timeout) = @_;
> - my $path = $class->filesystem_path($scfg, $volname);
> + my ($class, $scfg, $storeid, $volname, $timeout, $snap) = @_;
> + my $path = $class->filesystem_path($scfg, $volname, $snap);
>
> my $cmd = ['/sbin/lvs', '--separator', ':', '--noheadings', '--units',
> 'b',
> '--unbuffered', '--nosuffix', '--options', 'lv_size', $path];
> @@ -586,32 +679,180 @@ sub volume_size_info {
> }
>
> sub volume_snapshot {
> - my ($class, $scfg, $storeid, $volname, $snap) = @_;
> + my ($class, $scfg, $storeid, $volname, $snap, $running) = @_;
> +
> + my ($vmid, $format) = ($class->parse_volname($volname))[2,6];
> +
> + die "can't snapshot this image format\n" if $format ne 'qcow2';
> +
> + if ($running) {
> + #rename with blockdev-reopen is done at qemu level when running
> + $class->alloc_snap_image($storeid, $scfg, $volname, $snap);
> + if ($@) {
> + die "can't allocate new volume $volname: $@\n";
> + }
> + return;
> + }
> +
> + #rename current volume to snap volume
> + eval { $class->rename_volume($scfg, $storeid, $volname, $vmid, undef,
> 'current', $snap) };
> + die "error rename $volname to $snap\n" if $@;
> +
> + eval { $class->alloc_snap_image($storeid, $scfg, $volname, $snap) };
> + if ($@) {
> + my $err = $@;
> + eval { $class->rename_volume($scfg, $storeid, $volname, $vmid,
> undef, $snap, 'current') };
> + die $err;
> + }
> +}
> +
> +sub volume_rollback_is_possible {
> + my ($class, $scfg, $storeid, $volname, $snap, $blockers) = @_;
> +
> + my $snap_path = $class->path($scfg, $volname, $storeid, $snap);
>
> - die "lvm snapshot is not implemented";
> + $class->activate_volume($storeid, $scfg, $volname, undef, {});
> + my $snapshots = $class->volume_snapshot_info($scfg, $storeid, $volname);
> + my $parent_snap = $snapshots->{current}->{parent};
> +
> + return 1 if $parent_snap eq $snap;
> + die "can't rollback, '$snap' is not most recent snapshot on
> '$volname'\n";
> +
> + return 1;
> }
>
> +
> sub volume_snapshot_rollback {
> my ($class, $scfg, $storeid, $volname, $snap) = @_;
>
> - die "lvm snapshot rollback is not implemented";
> + my $format = ($class->parse_volname($volname))[6];
> +
> + die "can't rollback snapshot for this image format\n" if $format ne
> 'qcow2';
> +
> + $class->activate_volume($storeid, $scfg, $volname, undef, {});
> +
> + # we can simply reformat the current lvm volume to avoid
> + # a long safe remove.(not needed here, as the allocated space
> + # is still the same owner)
> + eval { lvm_qcow2_format($class, $storeid, $scfg, $volname, $format,
> $snap) };
> + if($@) {
> + die "can't rollback. Error reformating current $volname\n";
> + }
> + return undef;
> }
>
> sub volume_snapshot_delete {
> - my ($class, $scfg, $storeid, $volname, $snap) = @_;
> + my ($class, $scfg, $storeid, $volname, $snap, $running) = @_;
> +
> + my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
> $class->parse_volname($volname);
> +
> + die "can't delete snapshot for this image format\n" if $format ne
> 'qcow2';
> +
> + if ($running) {
> + $volname = $class->get_snap_volname($volname, $snap);
> + my $cleanup_worker = eval { $class->free_image($storeid, $scfg,
> $volname, $isBase, $format) };
> + die "error deleting snapshot $snap\n" if $@;
> +
> + if ($cleanup_worker) {
> + my $rpcenv = PVE::RPCEnvironment::get();
> + my $authuser = $rpcenv->get_user();
> + $rpcenv->fork_worker('imgdel', undef, $authuser, $cleanup_worker);
> + }
> + return;
> + }
>
> - die "lvm snapshot delete is not implemented";
> + my $cmd = "";
> + my $path = $class->filesystem_path($scfg, $volname);
> +
> + my $snapshots = $class->volume_snapshot_info($scfg, $storeid, $volname);
> + my $snappath = $snapshots->{$snap}->{file};
> + my $snapvolname = $snapshots->{$snap}->{volname};
> + die "volume $snappath is missing" if !-e $snappath;
> +
> + my $parentsnap = $snapshots->{$snap}->{parent};
> +
> + my $childsnap = $snapshots->{$snap}->{child};
> + my $childpath = $snapshots->{$childsnap}->{file};
> + my $childvolname = $snapshots->{$childsnap}->{volname};
> +
> + my $cleanup_worker = undef;
> + my $err = undef;
> + #if first snapshot,as it should be bigger, we merge child, and rename
> the snapshot to child
> + if(!$parentsnap) {
> + print "commit: merge content of $childpath into $snappath\n";
> + #can't use -d here, as it's an lvm volume
> + $cmd = ['/usr/bin/qemu-img', 'commit', $childpath];
> + eval { run_command($cmd) };
> + if ($@) {
> + die "error commiting $childpath to $snappath; $@\n";
> + }
> + print"delete $childvolname\n";
> +
> + $cleanup_worker = eval { $class->free_image($storeid, $scfg,
> $childvolname, 0) };
> + if ($@) {
> + die "error delete old snapshot volume $childvolname: $@\n";
> + }
> +
> + print"rename $snapvolname to $childvolname\n";
> + my $vg = $scfg->{vgname};
> + eval { lvrename($vg, $snapvolname, $childvolname) };
> + if ($@) {
> + warn $@;
> + $err = "error renaming snapshot: $@\n";
> + }
> +
> + } else {
> + #we rebase the child image on the parent as new backing image
> + my $parentpath = $snapshots->{$parentsnap}->{file};
> + print "rebase: merge diff content between $parentpath and $childpath
> into $childpath\n";
> + $cmd = ['/usr/bin/qemu-img', 'rebase', '-b', $parentpath, '-F',
> 'qcow2', '-f', 'qcow2', $childpath];
> + eval { run_command($cmd) };
> + if ($@) {
> + die "error rebase $childpath from $parentpath; $@\n";
> + }
> + #delete the snapshot
> + eval { $cleanup_worker = $class->free_image($storeid, $scfg,
> $snapvolname, 0); };
> + if ($@) {
> + die "error delete old snapshot volume $snapvolname\n";
> + }
> + }
> +
> + if ($cleanup_worker) {
> + my $rpcenv = PVE::RPCEnvironment::get();
> + my $authuser = $rpcenv->get_user();
> + $rpcenv->fork_worker('imgdel', undef, $authuser, $cleanup_worker);
> + }
> +
> + die $err if $err;
> }
>
> sub volume_has_feature {
> my ($class, $scfg, $feature, $storeid, $volname, $snapname, $running) =
> @_;
>
> my $features = {
> - copy => { base => 1, current => 1},
> - rename => {current => 1},
> + copy => {
> + base => { qcow2 => 1, raw => 1 },
> + current => { qcow2 => 1, raw => 1},
> + snap => { qcow2 => 1 },
> + },
> + 'rename' => {
> + current => { qcow2 => 1, raw => 1},
> + },
> + snapshot => {
> + current => { qcow2 => 1 },
> + snap => { qcow2 => 1 },
> + },
> +# fixme: add later ? (we need to handle basepath, volume activation,...)
> +# template => {
> +# current => { raw => 1, qcow2 => 1},
> +# },
> +# clone => {
> +# base => { qcow2 => 1 },
> +# },
> };
>
> - my ($vtype, $name, $vmid, $basename, $basevmid, $isBase) =
> +
> + my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
> $class->parse_volname($volname);
>
> my $key = undef;
> @@ -620,7 +861,7 @@ sub volume_has_feature {
> }else{
> $key = $isBase ? 'base' : 'current';
> }
> - return 1 if $features->{$feature}->{$key};
> + return 1 if defined($features->{$feature}->{$key}->{$format});
>
> return undef;
> }
> @@ -745,4 +986,18 @@ sub rename_volume {
> return "${storeid}:${target_volname}";
> }
>
> +sub get_snap_name {
> + my ($class, $volname, $snapname) = @_;
> +
> + my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
> $class->parse_volname($volname);
> + $name = !$snapname || $snapname eq 'current' ? $name :
> "snap-$snapname-$name";
> + return $name;
> +}
> +
> +sub get_snap_volname {
> + my ($class, $volname, $snapname) = @_;
> +
> + return $class->get_snap_name($volname, $snapname);
> +}
> +
> 1;
> --
> 2.39.5
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