To Tier or Not to Tier?

In my previous post, I discussed how storage virtualization capabilities are radically changing how we design and manage storage systems.  For a while now, I’ve been skeptical of the idea that paying per/TB for virtualization software can save me money over what would otherwise be hardware costs alone.

I decided to actually run some numbers and share my findings in this post.  To keep the numbers simple, I’m just looking at the hardware and software cost of the drives themselves and factored everything at list price.  This makes the calculations easier—although there are some caveats I’ll mention later in the post.  For the pricing information, I decided to use EMC’s price list for my VMAX configurations below, as it is already public knowledge in a google search.

For the first configuration I set a target capacity of 100TB (RAW).  I configured what I consider to be an average FAST (Fully Automated Storage Tiering) pool mix with 5% SSD, 20% 15K, and the remaining 75% as SATA drives.  You can see the details of my configuration below.


This 100TB FAST configuration resulted in 93K IOPs, 132 drives slots and price tag of $1,052,850.

I then recreated the configuration subtracting the would-be FAST costs and selecting an entire pool of 300GB 15K Drives.


This 100TB Non-FAST configuration totaled 61K IOPs, 340 drives and a price tag of $1,044,800. The FAST Configuration offered 34% more IOPs, 61% fewer drives and cost roughly the same as the traditional pool.

To be completely honest, I’m actually a bit surprised at the results. I was fully expecting to find that the “virtualization tax” added to FAST configurations added more in software cost than it reduced in hardware. While this is still true in some configurations—I found that, for most mixed-workloads, it will almost always make sense to buy FAST.

Final Thoughts:

In a real world config, the additional drives in the non-FAST solution would require additional enclosures and cabinets that would increase the cost well beyond the FAST configuration. The smaller footprint of the FAST config would also reduce facilities cost.

SSDs factored into half the cost of the FAST solution.  As the price of SSD drives fall, the value provided through virtualization software will continue to increase.

To achieve the IOPs in the FAST solution, over 80% of your IOPs must occur on the 5TB of SSD capacity.  This means if you require IOPs over a large dataset area—in other words, you have a low I/O density—your applications may run very poorly on FAST.  Be sure to understand your I/O profile before investing!

Finally, if you like the capabilities of FAST, want to stick with EMC, and don’t need performance or scale of a 6-9’s VMAX array, you could look into a comparable VNX system.  VNX systems offer similar (arguably more) features and the 5300 model doesn’t charge per/TB pricing.  Incredible value at a small fraction of the cost, if you can live with the more limited scale (125 Drives).

Be sure to do your research for virtualization and non-virtualization capabilities with all your vendors.  Some vendors are better than others when it comes to comparing pricing.

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