Testing disk speed... what is the best method?

I know that people use the "dd command" to measure disk write speed but others say you should measure iops instead. What is the best way to test the disk speed for real world use of a database being read and written to?

By putting a test DB on it.

Disk I/O testing is annoyingly a misrepresentation of what is going on.

Most writes to disks are small and quick, DD tests dont do that.

IOping is nice, but once again it is localized to one place at one time.

It isn't like a DB where you will have a read here, a write there, a more important read over there. etc.

My suggestion is find a host with SSDs and go with them if you are using it for a large DB.

I would also suggest, if it fits your budget, to offload the database on a single ssd vps, and connect to it remotely. that way you will get the best performance

mount -o remount /partition

run dd.. 

when you remount the partition the VFS cache layer is blown up and rebuilt, otherwise you won't get consistent results.

zionvps said:

I would also suggest, if it fits your budget, to offload the database on a single ssd vps, and connect to it remotely. that way you will get the best performance

Click to expand...

Best to do this over a private network for low latency.

open up the disk and look at it spin.

count the number of spins per second.

It's really difficult to test as others have mentioned, but I like using things like iozone and bonnie that can get some pretty random work going all at once.