A Closer Look at ZFS, Vdevs and Performance
When looking at the mails and comments I get about my ZFS optimization and my RAID-Greed posts, the same type of questions tend to pop up over and over again. Here’s an example from a reader email: “I was reading about ZFS on your blog and you mention that if I do a 6 drive array for example, and a single RAID-Z the speed of the slowest drive is the maximum I will be able to achieve, now I thought that ZFS would be better in terms of speed. Please let me know if there is a newer ZFS version that improved this or if it does not apply anymore.” This is just an example, but the basic theme is the same for much for the reactions I see: Many people think that RAID-Z will give them always good performance and are surprised that it doesn’t, thinking it’s a software, an OpenSolaris or a ZFS issue.
In reality, it’s just pure logic and physics, and to understand that we should look a little closer at what vdevs are in ZFS and how they work.