write block size - ssd

Lukas1234

Hello

I have a problem with understanding write block size.

Writes on ssd volume, type is ext4 block size to 4096, lsblk (PHY-SEC) for volume gives me 512

I run

dd if=/dev/urandom of=output2 obs=512000 conv=fsync count=10000000

and after that i run

dd if=/dev/urandom of=output2 obs=512 conv=fsync count=100000000

and the graph is identical.

I expected significant differences, what i miss ?

How to simulate change write block size ?

In some situations on real data, write block size above 150KB increases my response write even above 10ms.

Examples from dd want to understand what is going on.

Pavel

Hi,

block size is determined by: data rate/IOPS

Do you see increase of data rate and IOPS during on your volume during your test?

Lukas1234

I didn't know that, thank you

I thought it was layer 7, application in different block size gives data to write.

But then I didn't understand the block size on the file system, which doesn't change.

Thank you for explanation