ODX–Not All SANs Are Created Equally

I recently got to play with a very expensive fiber channel SAN for the first time in a while (I normally only see iSCSI or SAS in the real world).  This was a chance to play with WS2012 Hyper-V on this SAN, and this SAN supported Offloaded Data Transfer (ODX).

Put simply, ODX is a SAN feature that allows Windows to offload certain file operations to the SAN, such as:

  • Server to server file transfer/copy
  • Creating a VHD file

That latter was of interest to me, because this should accelerate the creation of a fixed VHD/X file, making (self-service) clouds more responsive.

The hosts were fully patched, both hotfixes and update rollups.  Yes, that includes the ODX hotfix that is bundled into the May clustering bundle.  We created a 60 GB fixed size VHDX file … and it took as long as it would without ODX.  I was afraid of this.  The manufacturer of this particular SAN has … a certain reputation for being stuck in the time dilation of an IT black hole since 2009.

If you’re planning on making use of ODX then you need to understand that this isn’t like making a jump from 1 Gbps to 10 Gbps where there’s a predictable 10x improvement.  Far from it; the performance of ODX on one vendors top end SAN can be very different to that of another manufacturer.  Two of my fellow Hyper-V MVPs have done a good bit of work looking into this stuff.

Hans Vredevoort (@hvredevoort) tested the HP 3PAR P10000 V400 with HP 3PAR OS v3.1.2.  With ODX enabled (it is by default on the SAN and WS2012) when creating a pretty regular 50 GB VHDX Hans saw the time go from an unenhanced 6.5 minutes to 2.5 minutes.  On the other hand, a 1 TB VHDX would take 33 minutes with ODX enabled.

Didier Van Hoye (@workinghardinit) decided to experiment with his Dell Compellent.  Didier created 10 * 50 GB VHDX files and 10 * 475 GB fixed VHDX files in 42 seconds.  That was 5.12 TB of files created nearly 2 minutes faster than the 3PAR could create a single 50 GB VHDX file.  Didier has understandably gone on a video recording craze showing off how this stuff works.  Here is his latest.  Clearly, the Compellent rocks where others waltz.

These comparisons reaffirm what you should probably know: don’t trust the whitepapers, brochures, or sales-speak from a manufacturer.  Evidently not all features are created equally.

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