If you’re reading consumer SSD reviews and using them to estimate SSD performance under database workloads, you’d better stop. Databases are not your typical consumer applications and they do not use IO in the same way.

Let’s look, for example, at this excellent AnandTech review of Samsung 960 Pro –  a consumer NVMe device that I happen to have in my test lab.

The summary table is actually great, showing the performance both at Queue Depth 1 (single threaded) as well as Queue Depth 32 – a pretty heavy concurrent load.

Even at QD1 we see 50K (4K) writes per second, which should be enough for pretty serious database workloads.

In reality, though, you might be in for some disappointing surprises. While “normal” buffered IO is indeed quite fast, this drive really hates fsync() calls, with a single thread …

In this blog post, I’ll look for the bottleneck that prevented the performance in my previous post from achieving better results.

The powerful machine I used in the tests in my previous post has a comparatively slow disk, and therefore I expected my tests would hit a point when I couldn’t increase performance further due to the disk speed.

Hardware configuration:

Processors: physical = 4, cores = 72, virtual = 144, hyperthreading = yes
Memory: 3.0T
Disk speed: about 3K …

This week with a client I saw ext4 used for the first time on a production MySQL system which was running Ubuntu 9.10 (Karmic Koala). I observe today while installing 9.10 Server locally that ext4 is the default option. The ext4 filesystem is described as better performance, reliability and features while there is also information about improvements in journaling.

At OSCON 2009 I attended a presentation on Linux Filesystem Performance for Databases by Selena Deckelmann in which ext4 was included. While providing some improvements in sequential reading and writing, there were issue with random I/O which is the key for RDBMS products.

Is the RAID configuration (e.g. RAID 5, RAID 10), strip size, buffer caches, LVM …