[Discuss] Failing WD Disks

[Kent Borg]

On 5/18/23 16:05, Rich Pieri wrote:
> I don't know if this is what happened
> on Kent's system or not. There are lots of reasons why I/O performance
> can change

It is faster compared to a different machine, a few years ago.


The reason I wanted fast random data was to paint a new disk with random 
bits before setting up an encrypted disk. The previous machine would 
have had:

  - slower (32-bit?) CPU and RAM.

  - slower USB hardware to disk (I seem to remember ~50MB/s)

  - older kernel with completely different random.c


At that point trying to dd from /dev/urandom to an external disk, 
/dev/urandom was the bottleneck, a lot slower than the disk. I even 
wrote a hacky RNG in Python to speed it up: Encrypt a counter, using a 
key from /dev/urandom, rollover the key every few gigabytes or so. (This 
RNG approach was not my invention, it is classic, and I used a Python 
library to do the encryption, so the stuff in the middle was not that 
dangerous a thing for me to program, and not a critical usage if I got 
it wrong.)

I conclude that random.c implemented a much slower /dev/urandom than 
does the version I have now. But maybe my current CPU is much better at 
running this code.

Heck, the Raspberry Pi 4 I tested on today produces urandom data much 
faster than the old bandwidth to disk I remember.


-kb, the Kent who is currently running current stable Debian, amd64.