Capacity Planning for Data Domain DD510 and DD530 Appliances

 I am slowly learning the models, options and capacities of the Data Domain line now that EMC has swallowed them up.  In this week’s post I want to take a look at the 500 series appliances with the way the drives are configured and note some things to think about.

There are 3 models in the 500 series line, the DD510, DD530 and DD565.  The DD565 is the first model of the DD line that can be expanded with extra disk trays so for this blog I’ll exclude it from the discussion.  The DD510 and DD530 are available either with 9 drives or 15 drives based on the capacity you need.  Once you hit 15 drives that’s it and you have to buy another appliance. They can be purchased initially with 9 drives and then upgraded with an additional 6 drives or purchased fully populated with 15 drives.  In most cases, people will tend to buy what they need now and then expand if necessary.  In most cases that is a good plan but you should take a close look at your data growth before you choose the 9 drive option and then upgrade later.  In this particular case 9+6 does not equal 15 exactly.  DD appliances are configured using RAID6 (dual parity).  When you purchase the lower capacity models with 9 drives those 9 drives are installed in a RAID6 configuration including 2 parity drives and a hot spare.  When you purchase the 6 drive expansion to increase your available space the now 15 drives are not reconfigured into a 15 drive RAID6 set.  Instead, the additional 6 drives are added in a completely new RAID6 set.  So now you end up with 4 parity drives instead of two.  Realistically, does this have a huge impact in your available space?  If you consider a 20:1 de-duplication ratio, YES.  The raw space difference may only be 1TB or 2TB depending on the model, but multiply that times 20 and you’re talking an extra 20 to 40TB+ of additional backup storage.

So if you are looking at a mid-size Data Domain solution you should really take a look at your projected data growth.  If you know you are going to have to expand beyond the standard 9 drive configuration in the near future it might be a good idea to just go ahead and buy the 15 drive configuration up front and gain the additional space.



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