Re: File sink causes "S" errors

Hi Thomas,

You may not be getting an accurate picture of your sustained write
throughput using dd.
Since you are using ext4, I’m assuming you are using Linux :slight_smile:
Linux does a good job caching to RAM before writing to disk, so when you
write only 1GB using dd, you are mostly exercising your RAM (assuming
have a normal amount of RAM).
If you run a test writing a file much larger than your RAM, you should
something closer to your true sustained write speed.

For example, I get the following results running your test, which make
caching very obvious:

[ Desktop]$ dd if=/dev/zero of=/home/amadsen/test.bin bs=10K
100000+0 records in
100000+0 records out
1024000000 bytes (1.0 GB) copied, 2.62228 s, 391 MB/s

If I increase the amount by a factor of 10, the system is forced to
write to disk finally and the throughput falls:

[Desktop]$ dd if=/dev/zero of=/home/amadsen/test.bin bs=100K
100000+0 records in
100000+0 records out
10240000000 bytes (10 GB) copied, 77.4247 s, 132 MB/s

Here is a site I use for checking out drive performance, there is a lot
difference between different SSDs.,2314.html

Good luck!