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, Iā€™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!