diff options
Diffstat (limited to 'qemu-options.hx')
| -rw-r--r-- | qemu-options.hx | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/qemu-options.hx b/qemu-options.hx index d86815dc04..35d95d1d89 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -133,7 +133,7 @@ ETEXI DEF("drive", HAS_ARG, QEMU_OPTION_drive, "-drive [file=file][,if=type][,bus=n][,unit=m][,media=d][,index=i]\n" " [,cyls=c,heads=h,secs=s[,trans=t]][,snapshot=on|off]\n" - " [,cache=writethrough|writeback|none|unsafe][,format=f]\n" + " [,cache=writethrough|writeback|none|directsync|unsafe][,format=f]\n" " [,serial=s][,addr=A][,id=name][,aio=threads|native]\n" " [,readonly=on|off]\n" " use 'file' as a drive image\n", QEMU_ARCH_ALL) @@ -164,7 +164,7 @@ These options have the same definition as they have in @option{-hdachs}. @item snapshot=@var{snapshot} @var{snapshot} is "on" or "off" and allows to enable snapshot for given drive (see @option{-snapshot}). @item cache=@var{cache} -@var{cache} is "none", "writeback", "unsafe", or "writethrough" and controls how the host cache is used to access block data. +@var{cache} is "none", "writeback", "unsafe", "directsync" or "writethrough" and controls how the host cache is used to access block data. @item aio=@var{aio} @var{aio} is "threads", or "native" and selects between pthread based disk I/O and native Linux AIO. @item format=@var{format} @@ -199,6 +199,10 @@ The host page cache can be avoided entirely with @option{cache=none}. This will attempt to do disk IO directly to the guests memory. QEMU may still perform an internal copy of the data. +The host page cache can be avoided while only sending write notifications to +the guest when the data has been reported as written by the storage subsystem +using @option{cache=directsync}. + Some block drivers perform badly with @option{cache=writethrough}, most notably, qcow2. If performance is more important than correctness, @option{cache=writeback} should be used with qcow2. |