With the 'blockdev' command line option, the cache options are split
up. While cache.direct and cache.no-flush can be set in the -blockdev
options, cache.writeback is a front-end property and was intentionally
removed from the 'blockdev' options by QEMU commit aaa436f998 ("block:
Remove cache.writeback from blockdev-add"). It needs to be configured
as the 'write-cache' property for the ide-hd/scsi-hd/virtio-blk
device.
Table from 'man kvm':
┌─────────────┬─────────────────┬──────────────┬────────────────┐
│ │ cache.writeback │ cache.direct │ cache.no-flush │
├─────────────┼─────────────────┼──────────────┼────────────────┤
│writeback │ on │ off │ off │
├─────────────┼─────────────────┼──────────────┼────────────────┤
│none │ on │ on │ off │
├─────────────┼─────────────────┼──────────────┼────────────────┤
│writethrough │ off │ off │ off │
├─────────────┼─────────────────┼──────────────┼────────────────┤
│directsync │ off │ on │ off │
├─────────────┼─────────────────┼──────────────┼────────────────┤
│unsafe │ on │ off │ on │
└─────────────┴─────────────────┴──────────────┴────────────────┘
Suggested-by: Alexandre Derumier <alexandre.derum...@groupe-cyllene.com>
Signed-off-by: Fiona Ebner <f.eb...@proxmox.com>
---
PVE/QemuServer.pm | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
index 82304096..f9e1b3f9 100644
--- a/PVE/QemuServer.pm
+++ b/PVE/QemuServer.pm
@@ -1317,6 +1317,8 @@ sub print_drivedevice_full {
my $device = '';
my $maxdev = 0;
+ my $machine_version = extract_version($machine_type, kvm_user_version());
+
my $drive_id = PVE::QemuServer::Drive::get_drive_id($drive);
if ($drive->{interface} eq 'virtio') {
my $pciaddr = print_pci_addr("$drive_id", $bridges, $arch,
$machine_type);
@@ -1327,7 +1329,6 @@ sub print_drivedevice_full {
my ($maxdev, $controller, $controller_prefix) = scsihw_infos($conf,
$drive);
my $unit = $drive->{index} % $maxdev;
- my $machine_version = extract_version($machine_type,
kvm_user_version());
my $device_type = PVE::QemuServer::Drive::get_scsi_device_type(
$drive, $storecfg, $machine_version);
@@ -1403,6 +1404,15 @@ sub print_drivedevice_full {
$device .= ",serial=$serial";
}
+ if (min_version($machine_version, 10, 0)) {
+ if (!drive_is_cdrom($drive)) {
+ my $write_cache = 'on';
+ if (my $cache = $drive->{cache}) {
+ $write_cache = 'off' if $cache eq 'writethrough' || $cache eq
'directsync';
+ }
+ $device .= ",write-cache=$write_cache";
+ }
+ }
return $device;
}
--
2.39.5
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