Storage 101

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Healthcare facilities beware. Data storage systems can be one of the greatest expenses for many picture archiving and communications system implementations. Cost is contingent upon the number of choices required to design and implement a PACS archive, which are many since all archives need two levels of storage: short-term and long-term. Providers needn't overbuy or under buy and must always keep in mind the declining cost of storage and the potential increase in patient data and images.

Different levels of storage exist within the framework of a PACS archive. The first level is a temporary directory that receives the files directly from the imaging modality. The amount of time the study resides there depends on the storage architecture of the organization. The application "talks" with the modalities and is responsible for reformatting the data and sending it to a more permanent form of storage, where it is then housed for a length of one to two years.

This rung on the PACS storage ladder is referred to as short term or online storage. There, electronic PACS images are typically stored for 12 to 18 months on fast-access, spinning disc media, such as RAID (redundant array of inexpensive disks) with a retrieval rate of two to five seconds. Another copy of the study is automatically written to a long-term storage device (near line storage) for both state retention mandates and disaster recovery. This allows the short-term archive to "purge" itself of unneeded data after reaching a capacity of 80 percent.

Providers agree that two years' worth of digital images in short-term storage is sufficient. "If you have 12 to18 months [of] short-term, then you are going to have 95 percent of all the images you want on the storage," says Richard Howe, PhD, vice president of information technology (IT) consulting for VHA Inc., a healthcare cooperative. Depending on the size of the facility, the number of modalities connected to the PACS, the retention time needed for the data and patient demographics, short-term storage capacities consist of multiple terabytes, with the option of scalability for increases in image volume.

As a vehicle to actually access the storage, PACS archives typically deploy the use of some form of networked storage, such as SAN (storage attached network) or NAS (network attached storage). SAN is a dedicated network for connecting storage devices to computers, while NAS is not directly attached to the servers and the storage is accessed using network standard protocols. The benefit of networked storage is that its capacity can be increased without interruptions to systems and workflow. The two differ in cost; SANs are about two and a half times more expensive than NAS because they require dedicated networks and gigabyte switches that are fairly expensive.

"You can acquire one terabyte of NAS storage for less than $15,000, which continues to drop," says Thomas Hough, principal of True North Consulting & Associates Inc. "You can acquire one terabyte of SAN storage for under $20,000 with additional terabytes costing less than $10,000. NAS tends to work well with large diagnostic imaging exam data sets. NAS will store the data and allow it to be retrieved very quickly. The only bottle neck in that process is the size of the network pipe going in to the NAS. It can be a little slower than a SAN in terms of delivering images."


When providers utilize networked storage, whether its SAN or NAS, they are enhancing the performance level of their archive. Orlando Regional Healthcare System (ORHS) is a not-for-profit healthcare network in Florida. Totaling 1,572 beds, ORHS consists of seven hospital facilities, M.D. Anderson Cancer Center Orlando and several ancillary organizations. GE Healthcare's Centricity PACS is in the process of deployment at ORHS and they just acquired new enterprise storage systems from IBM Inc. for radiology. "The infrastructure is in place, now it is just a matter of installing both the short-term and long-term storage throughout the organization," says John Berghuis, IS director of technology at ORHS.

Taking a centralized management approach to PACS, all of short-term storage will be deployed on IBM's TotalStorage Enterprise Storage Server (ESS) Shark 800 SAN. They are rolling out 22 TB for just PACS short-term and electronic images will be stored there for two years. Using an OC-48 fiber Sonnet Ring, all of the facilities will be connected via gigabit Ethernet. "We have implemented