Data Migration


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The Semperdata design inherently provides practical disaster recovery and data life management without the need for costly Disaster Recovery or Information Lifecycle Management platforms. A key assumption in the Semperdata design is that all information available for retrieval is stored on random-access (spinning) media. Offline copies on tape or optical disk media are only for purposes of disaster recovery or as input for future outbound migration.

Semperdata stores clinical data in DICOM media file-sets as large as the size of a DVD (4.7 Gigabytes). These data packages, when complete, are backed up onto LTO archive tapes or other supported media. The data on this backup volume is termed an Archive Parcel. Each Archive Parcel is labeled with a range of service dates for the clinical information it contains. When a Semperdata archive needs to be restored from these backup volumes, Semperdata reads them from newest to oldest, reporting on the system status Web page the range of dates that has been fully restored. With a single LTO-3 drive, Semperdata can restore over 2 Terabytes per day.

Semperdata support for data life management

Semperdata stores incoming patient data according to Retention Policy Groups (RPG), each with a set of retention rules. In the case of image data, the archive is configured with three RPGs:

Data in different RPGs are not commingled on archive media, although Pediatric or Indefinite policies can specify whether the data is also replicated in the Normal group. And optionally, the Pediatric and indefinite media file-sets (tomes) can be combined in the same archive parcels. The result of this separation is that there are separate archive media that contain the long-retention data.

Semperdata thus practically supports the culling of archive data according to institutional management policies. If the policy calls for the removal of adult data older 5 years old, the Semperdata data life management tool can, upon operator instructions, delete from Semperdata whole archive parcels with service date ranges outside the retention limits. The media volumes for those archive parcels can be retrieved from the shelf and discarded.

Unfortunately, there is not DICOM Standard message that can direct the main PACS archive to delete from its database the discarded studies, although there are proposals circulating in DICOM to define such messages. For the present, Semperdata creates a flat text list file that the PACS could use to cause such deletions. Laitek will implement DICOM deletion messages when they become available.