Slow disk io on MacOS

[IanButterworth]

Opening an issue to discuss the slow disk io performance seen in early tests across MacOS

[giordano]

On my MacBook, with macOS:

$ time dd if=/dev/zero bs=1k of=tstfile count=1
1+0 records in
1+0 records out
1024 bytes transferred in 0.000063 secs (16268816 bytes/sec)

real	0m0.007s
user	0m0.001s
sys	0m0.003s
$ time dd if=/dev/zero bs=1024k of=tstfile count=1
1+0 records in
1+0 records out
1048576 bytes transferred in 0.000707 secs (1483320914 bytes/sec)

real	0m0.005s
user	0m0.001s
sys	0m0.003s

with ArchLinux:

% time dd if=/dev/zero bs=1k of=tstfile count=1 
1+0 records in
1+0 records out
1024 bytes (1.0 kB, 1.0 KiB) copied, 0.000286261 s, 3.6 MB/s
dd if=/dev/zero bs=1k of=tstfile count=1  0.00s user 0.00s system 89% cpu 0.003 total
% time dd if=/dev/zero bs=1024k of=tstfile count=1  
1+0 records in
1+0 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.00084763 s, 1.2 GB/s
dd if=/dev/zero bs=1024k of=tstfile count=1  0.00s user 0.02s system 98% cpu 0.023 total