[pve-devel] [PATCH V2 pve-storage] lvm: use blkdiscard instead cstream to saferemove drive

[Alexandre Derumier via pve-devel <pve-devel@lists.proxmox.com>]

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From: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
To: pve-devel@lists.proxmox.com
Subject: [PATCH V2 pve-storage] lvm: use blkdiscard instead cstream to saferemove drive
Date: Thu, 14 Aug 2025 12:45:36 +0200
Message-ID: <20250814104536.943007-1-alexandre.derumier@groupe-cyllene.com>

Current cstream implementation is pretty slow as hell, even without throttling.

use blkdiscard --zeroout instead, which is lot of magnetude faster

Another benefit is that blkdiscard is skipping already zeroed block, so for empty
temp images like snapshot, is pretty fast.

blkdiscard don't have throttling like cstream, but we can tune the step size
of zeroes pushed to the storage.
I'm using 32MB stepsize by default , like ovirt, where it seem to be the best
balance between speed and load.
https://github.com/oVirt/vdsm/commit/79f1d79058aad863ca4b6672d4a5ce2be8e48986

but it can be reduce with "saferemove_stepsize" option.

Also adding an option "saferemove_discard", to use discard instead zeroing.

test with a 100G volume (empty):

time /usr/bin/cstream -i /dev/zero -o /dev/test/vm-100-disk-0.qcow2 -T 10 -v 1 -b 1048576

13561233408 B 12.6 GB 10.00 s 1356062979 B/s 1.26 GB/s
26021462016 B 24.2 GB 20.00 s 1301029969 B/s 1.21 GB/s
38585499648 B 35.9 GB 30.00 s 1286135343 B/s 1.20 GB/s
50998542336 B 47.5 GB 40.00 s 1274925312 B/s 1.19 GB/s
63702765568 B 59.3 GB 50.00 s 1274009877 B/s 1.19 GB/s
76721885184 B 71.5 GB 60.00 s 1278640698 B/s 1.19 GB/s
89126539264 B 83.0 GB 70.00 s 1273178488 B/s 1.19 GB/s
101666459648 B 94.7 GB 80.00 s 1270779024 B/s 1.18 GB/s
107390959616 B 100.0 GB 84.39 s 1272531142 B/s 1.19 GB/s
write: No space left on device

real    1m24.394s
user    0m0.171s
sys     1m24.052s

time blkdiscard --zeroout /dev/test/vm-100-disk-0.qcow2 -v
/dev/test/vm-100-disk-0.qcow2: Zero-filled 107390959616 bytes from the offset 0

real    0m3.641s
user    0m0.001s
sys     0m3.433s

test with a 100G volume with random data:

time blkdiscard --zeroout /dev/test/vm-100-disk-0.qcow2 -v

/dev/test/vm-112-disk-1: Zero-filled 4764729344 bytes from the offset 0
/dev/test/vm-112-disk-1: Zero-filled 4664066048 bytes from the offset 4764729344
/dev/test/vm-112-disk-1: Zero-filled 4831838208 bytes from the offset 9428795392
/dev/test/vm-112-disk-1: Zero-filled 4831838208 bytes from the offset 14260633600
/dev/test/vm-112-disk-1: Zero-filled 4831838208 bytes from the offset 19092471808
/dev/test/vm-112-disk-1: Zero-filled 4865392640 bytes from the offset 23924310016
/dev/test/vm-112-disk-1: Zero-filled 4596957184 bytes from the offset 28789702656
/dev/test/vm-112-disk-1: Zero-filled 4731174912 bytes from the offset 33386659840
/dev/test/vm-112-disk-1: Zero-filled 4294967296 bytes from the offset 38117834752
/dev/test/vm-112-disk-1: Zero-filled 4664066048 bytes from the offset 42412802048
/dev/test/vm-112-disk-1: Zero-filled 4697620480 bytes from the offset 47076868096
/dev/test/vm-112-disk-1: Zero-filled 4664066048 bytes from the offset 51774488576
/dev/test/vm-112-disk-1: Zero-filled 4261412864 bytes from the offset 56438554624
/dev/test/vm-112-disk-1: Zero-filled 4362076160 bytes from the offset 60699967488
/dev/test/vm-112-disk-1: Zero-filled 4127195136 bytes from the offset 65062043648
/dev/test/vm-112-disk-1: Zero-filled 4328521728 bytes from the offset 69189238784
/dev/test/vm-112-disk-1: Zero-filled 4731174912 bytes from the offset 73517760512
/dev/test/vm-112-disk-1: Zero-filled 4026531840 bytes from the offset 78248935424
/dev/test/vm-112-disk-1: Zero-filled 4194304000 bytes from the offset 82275467264
/dev/test/vm-112-disk-1: Zero-filled 4664066048 bytes from the offset 86469771264
/dev/test/vm-112-disk-1: Zero-filled 4395630592 bytes from the offset 91133837312
/dev/test/vm-112-disk-1: Zero-filled 3623878656 bytes from the offset 95529467904
/dev/test/vm-112-disk-1: Zero-filled 4462739456 bytes from the offset 99153346560
/dev/test/vm-112-disk-1: Zero-filled 3758096384 bytes from the offset 103616086016

real    0m23.969s
user    0m0.030s
sys     0m0.144s

Signed-off-by: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
---
 src/PVE/Storage/LVMPlugin.pm | 43 ++++++++++++++++--------------------
 1 file changed, 19 insertions(+), 24 deletions(-)

diff --git a/src/PVE/Storage/LVMPlugin.pm b/src/PVE/Storage/LVMPlugin.pm
index 0416c9e..0fcb7cc 100644
--- a/src/PVE/Storage/LVMPlugin.pm
+++ b/src/PVE/Storage/LVMPlugin.pm
@@ -287,35 +287,19 @@ my sub free_lvm_volumes {
     # we need to zero out LVM data for security reasons
     # and to allow thin provisioning
     my $zero_out_worker = sub {
-        # wipe throughput up to 10MB/s by default; may be overwritten with saferemove_throughput
-        my $throughput = '-10485760';
-        if ($scfg->{saferemove_throughput}) {
-            $throughput = $scfg->{saferemove_throughput};
-        }
         for my $name (@$volnames) {
             print "zero-out data on image $name (/dev/$vg/del-$name)\n";
 
+            warn
+                "The 'saferemove_throughput' option set for '${storeid}' is deprecated and will be removed."
+                if $scfg->{saferemove_throughput};
+            my $stepsize = $scfg->{saferemove_stepsize} // 32;
             my $cmd = [
-                '/usr/bin/cstream',
-                '-i',
-                '/dev/zero',
-                '-o',
-                "/dev/$vg/del-$name",
-                '-T',
-                '10',
-                '-v',
-                '1',
-                '-b',
-                '1048576',
-                '-t',
-                "$throughput",
+                '/usr/sbin/blkdiscard', "/dev/$vg/del-$name", '-v', '--step', "${stepsize}M",
             ];
-            eval {
-                run_command(
-                    $cmd,
-                    errmsg => "zero out finished (note: 'No space left on device' is ok here)",
-                );
-            };
+            push @$cmd, '--zeroout' if !$scfg->{saferemove_discard};
+
+            eval { run_command($cmd); };
             warn $@ if $@;
 
             $class->cluster_lock_storage(
@@ -376,6 +360,15 @@ sub properties {
             description => "Zero-out data when removing LVs.",
             type => 'boolean',
         },
+        saferemove_discard => {
+            description => "Wipe with discard instead zeroing.",
+            type => 'boolean',
+            default => 0,
+        },
+        saferemove_stepsize => {
+            description => "Wipe step size (default 32MB).",
+            enum => [qw(1 2 4 8 16 32)],
+        },
         saferemove_throughput => {
             description => "Wipe throughput (cstream -t parameter value).",
             type => 'string',
@@ -394,6 +387,8 @@ sub options {
         shared => { optional => 1 },
         disable => { optional => 1 },
         saferemove => { optional => 1 },
+        saferemove_discard => { optional => 1 },
+        saferemove_stepsize => { optional => 1 },
         saferemove_throughput => { optional => 1 },
         content => { optional => 1 },
         base => { fixed => 1, optional => 1 },
-- 
2.47.2



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