[pve-devel] qemu 1.2 :default cache mode writeback

Alexandre DERUMIER aderumier at odiso.com
Thu Sep 6 12:18:09 CEST 2012

I have found the commit, 
I'm not sure it's related to the host cache, but maybe more the cache inside the guest ?

"Now all major device models (IDE, SCSI, virtio) can choose between
writethrough and writeback at run-time, and virtio will even revert
to writethrough if the guest is not capable of sending flushes.  So
we can change the default to writeback at last.

Tested, for lack of a better idea, with a breakpoint on bdrv_open
and all cache choices one by one.

Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
 blockdev.c | 1 +
 1 file modificato, 1 inserzione(+)

diff --git a/blockdev.c b/blockdev.c
index 8669142..7c83baa 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -377,6 +377,7 @@ DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi)
+    bdrv_flags |= BDRV_O_CACHE_WB;
     if ((buf = qemu_opt_get(opts, "cache")) != NULL) {
         if (bdrv_parse_cache_flags(buf, &bdrv_flags) != 0) {
             error_report("invalid cache option");


----- Mail original ----- 

De: "Alexandre DERUMIER" <aderumier at odiso.com> 
À: pve-devel at pve.proxmox.com 
Envoyé: Jeudi 6 Septembre 2012 12:13:48 
Objet: [pve-devel] qemu 1.2 :default cache mode writeback 

I just see that in the release note: 

block: default cache mode is now writeback 

Maybe do we need to warn proxmox users and update pve-manager ? 

(default was cache=none if not defined) 

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