The Storage Economist

This is my 3^rd installment of a 4-part series on when/how it is cheaper to reclaim disk as opposed to buying new. The previous 2 entries covered the setup and calculations, now we will look at conditions when each tends to be better.

Just because you can virtualize and over-provision, doesn’t mean it is always an economically better approach. Sometimes you feel like a nut, sometimes you don’t. Sometimes it is cheaper to buy, sometimes it’s not.

There may be operational, non-cost and political reasons to do one thing or another, and in this case I will limit my comments to the economic differentiation of these 2 methods to present new capacity.

When is reclamation MOST LIKELY BETTER than buying new

• When the reclaim capacity is high enough to clear the bar relative to the reclamation overhead/tariff; this tends to be around 20-25TB, but can vary depending on many conditions
• When the reclaimed capacity is relatively new, and has good, useful life ahead
• If your reclamation approach can ingest heterogeneous storage
• The tier of storage to reclaim has some portion (the more the better) of tier 1 and 2
• Purchase prices are high, or supply is limited
• CAPEX budgets are under scrutiny
• You cannot afford the additional power, cooling and floor space for more arrays; since you are reclaiming capacity that is already being cooled and electrified, this is a good option
• Your CFO is measuring ROA and pressure to do more with less is a constant IT message
• You have confidence and some relative experience in storage virtualization, over-provisioning
• The data that you place in reclaimed capacity can, for the most part, be thinned

When is buying MOST LIKELY BETTER than reclaiming

• There is a SW and (some) HW overhead for virtualization and thin provisioning. Overhead might not be the best word, perhaps tariff is better; the savings in reclamation have to overcome the tariff related to advanced storage architecture that can produce reclaimed space and better ROA
  • Software licenses
  • Some appliance or controller upgrades
  • Services to perform the migration
  • Some architectures also require a host outage, some do not
• If the reclamation tariff is too high (prices and recurring costs of labor, maintenance), then the benefits may not be realized
• If the tier of storage is relatively low, then the value of the reclaimed disk (say tier 3 or 4) will not be worth the effort
• If the reclaim potential capacity is very low, and/or if the growth rate is very low
• If the reclaim-capacity disk array is very old, then the resulting power, cooling and potential maintenance cost per TB may not be worth reclaiming
• If the capacity that is desirable to reclaim is not centralized, then the network and latency may prohibit the effort to repatriate
• Your own management maturity and processes may exclude this kind of moderate operational and architectural capability. If you do not have a good CMDB, services catalog or SLA, then some of the steps necessary may be temporarily out of your reach

I have probably missed a couple of pro and con bullets above, your comments and additions would be most welcome.

My next entry will wrap this topic up, and provide some guidance on using secondary metrics around TCO to provide another view of comparing reclaim vs. buy.