Advatronix Cirrus 1200: a Storage Server Under Your Desk

Low latency database transactions test

Before we can start comparing the Cirrus 1200 to an alternative configuration, we must find out how we should configure our system. Indeed there are two cache levels, the RAM cache of the controller and the SSD cache, and both can be set to cache reading and/or writing. That gives us eight different configurations, though not all of them make sense of course.

There is a quirk in the Adaptec software. We first enabled Maxcache on a single SSD. Adaptec asked us whether we are sure (as SSDs can fail too) and when we answered "yes", all the software (BIOS and Maxview) reported proudly that SSD caching was enabled. It turned out that this was not the case at all. Only when we set the SSD to RAID-1 was Maxcache (SSD caching) properly enabled.

The results are somewhat surprising: once the Maxcache works properly, it seems that the RAID controller cache just adds latency. The RAID controller does help when the SSD does not accelerate writing, but with Maxcache active on the SSDs the RAID controller caching slows things down a bit.

The next question that we asked ourselves is whether it still matters to have lots of spinning disks behind the SSD cache. After all, the SSD cache seems to be doing all the hard work. So we replaced the eight Seagate 4TB drives in RAID-10 with a two disk system using RAID-1.

The performance gain of using eight spindles instead of two is pretty small, but it is still measureable. We show a 22% increase in the total number of transactions. In most small businesses this performance increase will not be enough to convince people to use this many disks on for a database. The RAID-1 setup is probably better as more disks can then be used for serving files and documents. This way, the storage capacity of the file server can be a lot bigger, which is a huge advantage. In most enterprises, file server capacity will be a much higher priority than a few procentagaes of extra database performance.