[PATCH qemu-server 3/3] vma restore: skip page cache on block devices backed by zfspool

[Christian Ebner <c.ebner@proxmox.com>]

Skip the host page cache for restores on zvols, as page writeback can
cause I/O delay on other ZFS-backed VMs on certain setups, as reported
in enterprise support and reproduced internally. The restored data is
not to be read back from cache during restore anyways.

Keep for other storage types to reduce regression potential.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
 src/PVE/QemuServer.pm | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
index 70d7d880..8ff52def 100644
--- a/src/PVE/QemuServer.pm
+++ b/src/PVE/QemuServer.pm
@@ -7672,8 +7672,15 @@ sub restore_vma_archive {
             }
 
             my $path = PVE::Storage::path($cfg, $volid);
+            my $scfg = PVE::Storage::storage_config($cfg, $storeid);
 
-            print $fifofh "${map_opts}format=$d->{format}:${write_zeros}:$d->{devname}=$path\n";
+            my $cache_none = '';
+            if ($scfg->{type} eq 'zfspool') {
+                $cache_none = ':cache=none';
+                print "skipping page cache for '$d->{devname}'\n";
+            }
+
+            print $fifofh "${map_opts}format=$d->{format}${cache_none}:${write_zeros}:$d->{devname}=$path\n";
 
             print "map '$d->{devname}' to '$path' (write zeros = ${write_zeros})\n";
         }
-- 
2.47.3