Are you a believer?

There are articles out there talking about the useless usage of dd and why cat is better. Cat is faster because it automatically adjusts the blocksize and dd is slow because it internally only works with 512 byte blocks. This and That.

I did some simple tests with time, dd and cat, added some obscure parameters to dd, because cat is better.

Testing dd with status and specific blocksize

 $ time dd if=/dev/sdd of=test.dd status=progress bs=8M
 15921577984 bytes (16 GB, 15 GiB) copied, 878 s, 18.1 MB/s 
 1899+1 records in
 1899+1 records out
 15931539456 bytes (16 GB, 15 GiB) copied, 879.018 s, 18.1 MB/s

 0.04s user 23.33s system 2% cpu 14:39.03 total

Testing dd

 $ dd if=/dev/sdd of=test.dd 
 31116288+0 records in
 31116288+0 records out
 15931539456 bytes (16 GB, 15 GiB) copied, 869.783 s, 18.3 MB/s
 16.13s user 159.22s system 20% cpu 14:29.80 total

Testingcat with pv

 $ time cat /dev/sdd | pv > test.raw
 14.8GiB 0:14:43 [17.2MiB/s] [        <=>                            ]
 0.28s user 25.84s system 2% cpu 14:43.18 total

Testing cat

 $ time dd if=/dev/sdd of=test.dd status=progress bs=8M
 15921577984 bytes (16 GB, 15 GiB) copied, 878 s, 18.1 MB/s 
 1899+1 records in
 1899+1 records out
 15931539456 bytes (16 GB, 15 GiB) copied, 879.018 s, 18.1 MB/s

 0.04s user 23.33s system 2% cpu 14:39.03 total

Testing dd

 $ dd if=/dev/sdd of=test.dd 
 31116288+0 records in
 31116288+0 records out
 15931539456 bytes (16 GB, 15 GiB) copied, 869.783 s, 18.3 MB/s
 16.13s user 159.22s system 20% cpu 14:29.80 total

Testing catwith pv

 $ time cat /dev/sdd | pv > test.raw
 14.8GiB 0:14:43 [17.2MiB/s] [        <=>                            ]
 0.28s user 25.84s system 2% cpu 14:43.18 total

Testing cat

 $ time cat /dev/sdd > test.raw
 0.18s user 21.21s system 2% cpu 14:42.25 total

Y U DO IT WRONG

Somehow my cat is not as fast as dd.

KTHBYE

I use Mosquitto as my main MQTT broker for my smart home environment. Recently I came across some behavior I should investigate further in near future.

The MQTT clients did not authenticate to broker with a correct password. But the clients were accepted, at least for a short period of time. After that the clients were disconnected. During this short time, the devices could receive and sent messages without being authenticated. hm…..