Re: [Libguestfs] Appliance image. Why raw?
On Tue, Jun 20, 2017 at 05:04:53PM +0300, Pavel Butsykin wrote:
I noticed that raw is intentionally used as image format for
appliance
image. So I would like to ask, is there any reason to use raw as image
format for appliance?
The simple answer is because we create the appliance image (it's an
ext2/3/4 filesystem) using e2fsprogs, and that library wouldn't know
how to create anything else since it always assumes it's writing
directly to a device.
https://github.com/libguestfs/supermin/blob/master/src/format_ext2.mli#L2...
HTH,
Rich.
I would suggest that choice is related with the performance, so I
did
several test runs (./run utils/boot-benchmark/boot-benchmark)
/appliance/root.raw:
Result: 1342.9ms ±2.9ms
Result: 1370.1ms ±17.3ms
Result: 1365.1ms ±11.0ms
appliance/root.qcow2:
Result: 1353.1ms ±2.4ms
Result: 1350.2ms ±5.3ms
Result: 1374.7ms ±5.4ms
But even theoretically there should not be much difference, because
qcow2 uses a cache to internal tables. Also -drive configured to use the
host cache:
if (has_appliance_drive) {
ADD_CMDLINE ("-drive");
ADD_CMDLINE_PRINTF ("file=%s,snapshot=on,id=appliance,"
"cache=unsafe,if=none,format=raw",
--
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