Virtio - writeback

root@didi:~# dd if=/dev/zero of=dados01.dat bs=16k count=51200 
51200+0 records in
51200+0 records out
838860800 bytes (839 MB) copied, 11.3943 s, 73.6 MB/s
root@didi:~# dd if=/dev/zero of=dados01d.dat bs=16k count=50240 oflag=direct
50240+0 records in
50240+0 records out
823132160 bytes (823 MB) copied, 11.7236 s, 70.2 MB/s

Virtio - none

root@didi:~# dd if=/dev/zero of=dados02.dat bs=16k count=51200 
51200+0 records in
51200+0 records out
838860800 bytes (839 MB) copied, 12.0715 s, 69.5 MB/s
root@didi:~# dd if=/dev/zero of=dados02b.dat bs=16k count=51200 oflag=direct
51200+0 records in
51200+0 records out
838860800 bytes (839 MB) copied, 27.9231 s, 30.0 MB/s

IDE - writeback

root@didi:~# dd if=/dev/zero of=dados03.dat bs=16k count=51200 
51200+0 records in
51200+0 records out
838860800 bytes (839 MB) copied, 3.42578 s, 245 MB/s
root@didi:~# dd if=/dev/zero of=dados03d.dat bs=16k count=51200 oflag=direct
51200+0 records in
51200+0 records out
838860800 bytes (839 MB) copied, 22.335 s, 37.6 MB/s

IDE - none

root@didi:~# dd if=/dev/zero of=dados04.dat bs=16k count=51200 
51200+0 records in
51200+0 records out
838860800 bytes (839 MB) copied, 13.8724 s, 60.5 MB/s
root@didi:~# dd if=/dev/zero of=dados04d.dat bs=16k count=51200 oflag=direct
51200+0 records in
51200+0 records out
838860800 bytes (839 MB) copied, 28.3395 s, 29.6 MB/s