> > > dd if=/path/to/iso-image of=/dev/sd? bs=4M status=progress > > > > Replace the obvious bits. > > I've tried a few values of block size over the years, but so far I haven't > noticed any difference. I haven't run any proper tests though. >
I think it's just that the default blocksize is (or was) very small (512 bytes?) so setting it to anything non-small helps a lot. eg one example (from https://superuser.com/questions/234199/good-block-size-for-disk-cloning-with-diskdump-dd#234204) seems to show that most gains are in by around 16k. There's probably a lot of testing noise in these results. $ ./dd_obs_test.sh block size : transfer rate 512 : 11.3 MB/s 1024 : 22.1 MB/s 2048 : 42.3 MB/s 4096 : 75.2 MB/s 8192 : 90.7 MB/s 16384 : 101 MB/s 32768 : 104 MB/s 65536 : 108 MB/s 131072 : 113 MB/s 262144 : 112 MB/s 524288 : 133 MB/s 1048576 : 125 MB/s 2097152 : 113 MB/s 4194304 : 106 MB/s 8388608 : 107 MB/s 16777216 : 110 MB/s 33554432 : 119 MB/s 67108864 : 134 MB/s
