Blackmagic Disk Speed Test showing slower results

We have been installing a new Xsan system the latest days (more about that in a later post). When testing the performance we use two different tools, and they have very different results, 186 MB/second vs 136 MB/second.

The first one is Xsan tuner, that comes with Xsan:

Xsan tuner

Speed is calculated to 186 MB/second.

We use DeckLink Extreme HD cards in the Macs (10 bits uncompressed SDI). Blackmagic also has their own test tool for disk speeds, the Blackmagic Disk Speed Test:

BlackMagic Disk Speed Test

Now, the same disks show 136 MB/second.

Which one to trust? BlackMagic make dead solid products, but on this one I hope their tools show the wrong results…

If you need to test your drives for speed, whether you use BlackMagic cards or not, download the DeckLink drivers for Mac OS X or Windows XP, and you’ll get the Blackmagic Disk Speed Test application when you install it. If you don’t need the actual drivers, just “hide away” the app, and uninstall the drivers again.

Xsan tuner can be downloaded from

Why a difference?

Do you have any idea why the two apps show different speeds? 136 MB/second up to 186 MB/second is almost two more streams of uncompressed video in realtime. Less rendering, more done.