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=== Description (from pull-request) ===
When taking snapshots of running VMs on BTRFS backed filesystems this was causing issues when doing BTRFS volume send/recv.
See https://discuss.linuxcontainers.org/t/running-virtual-machines-with-lxd-4-0/7519/98
Signed-off-by: Thomas Parrott <thomas.parr...@canonical.com>
From d67a7eb0e233148cf12d17138f786e0df41a226f Mon Sep 17 00:00:00 2001
From: Thomas Parrott <thomas.parr...@canonical.com>
Date: Wed, 16 Sep 2020 11:23:41 +0100
Subject: [PATCH] lxd/instance/drivers/driver/qemu: Switch to threads locking
mode and writeback cache mode for BTRFS
When taking snapshots of running VMs on BTRFS backed filesystems this was
causing issues when doing BTRFS volume send/recv.
Signed-off-by: Thomas Parrott <thomas.parr...@canonical.com>
---
lxd/instance/drivers/driver_qemu.go | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/lxd/instance/drivers/driver_qemu.go
b/lxd/instance/drivers/driver_qemu.go
index c3b3d80d35..00c9847198 100644
--- a/lxd/instance/drivers/driver_qemu.go
+++ b/lxd/instance/drivers/driver_qemu.go
@@ -2041,11 +2041,14 @@ func (vm *qemu) addDriveConfig(sb *strings.Builder,
bootIndexes map[string]int,
return errors.Wrapf(err, "Failed detecting filesystem
type of %q", driveConf.DevPath)
}
- // If FS is ZFS, avoid using direct I/O and use host page cache
only.
- if fsType == "zfs" {
+ // If backing FS is ZFS or BTRFS, avoid using direct I/O and
use host page cache only.
+ // We've seen ZFS hangs and BTRFS checksum issues when using
direct I/O on image files.
+ if fsType == "zfs" || fsType == "btrfs" {
if driveConf.FSType != "iso9660" {
- logger.Warnf("Using writeback cache I/O with
%s", driveConf.DevPath)
+ // Only warn about using writeback cache if the
drive image is writable.
+ logger.Warnf("Using writeback cache I/O with %q
as backing filesystem is %q", driveConf.DevPath, fsType)
}
+
aioMode = "threads"
cacheMode = "writeback" // Use host cache, with neither
O_DSYNC nor O_DIRECT semantics.
}
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