Default to virtio system disks

The qcow2 + virtio + writeback problem seems to be fixed.

Signed-off-by: Martin Schwenke <martin@meltin.net>

1 files changed, 19 insertions, 7 deletions

diff --git a/README b/README
index 96c9840..73fb7a7 100644
--- a/README
+++ b/README
@@ -440,6 +440,19 @@ Keep it simple
   CTDB cluster.  It is just extra node that can be used as a test
   client or similar.
 
+Corrupt system disks
+====================
+
+Recent versions of KVM seem to have fixed problems where the
+combination of qcow2 file format, virtio block devices and writeback
+caching would cause result in corrupt.  This means the default system
+disk bus type (a.k.a. SYSTEM_DISK_TYPE) is now virtio.
+
+If using an older version of KVM or if you experience corruption of
+the system disk, try using IDE system disks:
+
+  SYSTEM_DISK_TYPE=ide
+
 iSCSI shared disks
 ==================
 
@@ -476,13 +489,12 @@ cluster will need to have a different setting for ISCSI_TID.
 Raw IDE system disks
 ====================
 
-RHEL versions of KVM do not support the SCSI block device emulation,
-so autocluster now defaults to using an IDE system disk instead of a
-SCSI one.  Therefore, you can use virtio or ide system disks.
-However, writeback caching, qcow2 and virtio are incompatible and
-result in I/O corruption.  So, you can use either virtio system disks
-without any caching, accepting reduced performance, or you can use IDE
-system disks with writeback caching, with nice performance.
+Older RHEL versions of KVM did not support the SCSI block device
+emulation, and produced corruption when virtio disks were used with
+qcow2 disk images and writeback caching.  In this case, you can use
+either virtio system disks without any caching, accepting reduced
+performance, or you can use IDE system disks with writeback caching,
+with nice performance.
 
 For IDE disks, here are the required settings: