Cloud storage for archiving


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Service is the critical factor

Service-level management, then, is critical to the initial decision for cloud archiving as well as ongoing operations. When shopping for a cloud archival vendor, consider the following service-level issues:

Uptime. For most applications, three nines or four nines of availability are sufficient to meet business requirements. If you need five nines, you probably have data access requirements that aren’t conducive to an archive tier. Data hosted in an archive tier is, by definition, non-critical. The uptime requirement largely determines how much infrastructure the vendor must provision, so it has a big impact on the hosting cost. Don’t guess; determine the actual hours when data will be accessed, access patterns and cost of downtime. These calculations can be compared to the cost of various uptime guarantees, and easily justified or rejected based on the comparison. Vendors often offer hosting-fee rebates or other performance penalties for missing

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service-level agreements (SLAs). However, the caveats are contained in the fine print, so read them.

Accessibility. Accessibility and uptime aren’t necessarily the same. The storage may be humming, but the subcomponents render an application unavailable. If you need redundancy or multiple redundancy of data links, for example, you’ll have to pay for them but the alternative may be unacceptable application outages. Make sure service levels encompass end-to-end data availability.

Performance. Quantify how many IOPS your applications require and ensure this number is part of the SLA. IOPS can be measured either as an average or during peak activity. If you demand IOPS guarantees at peak, then you’ll have to pay for the vendor to provision them. Some vendors may offer metered billing, but many organizations don’t like the potential uncertainty of such billing should demand suddenly spike. Most organizations will absorb a certain amount of constrained operation (especially for an archive tier) in return for cost certainty. In this case, the SLA is for guaranteed IOPS, not absolute performance experienced by the end user. If application demands exceed contracted IOPS capacity, it’s rightly the IT organization’s problem; additional IOPS can always be purchased.

Data recoverability. As they do for in-house applications, IT organizations need to specify recovery point objective (RPO) and recovery time objective (RTO) requirements for cloud-based archives. This is related to uptime, but also covers contingencies such as data corruption or a component failure that doesn’t affect overall uptime but impacts individual applications. The vendor should have default values for RPO and RTO, which may be sufficient for an archive tier. Again, don’t guess. Know what kind of data loss and application unavailability the business units can financially tolerate. In many cases, it’s much more than is intuitive.

Disaster recovery (DR). If the cloud archive is used as off-site replicated storage to satisfy data redundancy requirements, it may not be necessary to consider a DR strategy for this tier. But buyer beware: Most hosted storage doesn’t include any DR contingency. If the hosted data is “live” data provisioned as hybrid cloud storage, then a DR plan may be necessary. Hosting providers may regularly back up the data, but they generally don’t rotate the data off-site, and if they do, they do so infrequently (e.g., monthly). Although a disaster at a SAS-70 compliant data center is unlikely, it’s not impossible. DR capability from a hosting company is often a significant additional expense and can change the economics of hosting in a hurry. Make sure data isn’t left in a vulnerable state.

Backup and recovery. Even if the hosting vendor backs up the data regularly and rotates it off-site frequently, IT organizations may not be out of the woods. Hosting companies usually have a limited number of backup software options and tape technologies. This means their backup format (hardware, software or both) may be incompatible with your IT systems. If an IT organization is forced to do a recovery from the vendor’s tapes, there could be a substantial delay in acquiring the necessary infrastructure. Ensure there’s a way out in a worst-case scenario.

Compliance. Archived data that requires special compliance treatment may still be a candidate for cloud hosting. You’ll need to ensure the data is retained on immutable media, if required. You’ll probably also need assurance that strict access guidelines are followed and auditable; SAS-70 providers should have such processes in place.

Cost certainty and granularity. One of the key benefits to cloud storage hosting for archiving rather than using in-house infrastructure is that you pay only for the storage consumed. The metering should go up or down with use, though it may have a floor minimum.

This was first published in May 2012

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