PDS Architecture
PDS is a novel storage architecture with built-in support for long-term digital preservation based on OAIS. In contrast with traditional block or file storage, and even with traditional archival systems, PDS realizes the logical concept of a preservation information object, namely the OAIS AIP, into a physical storage object.
PDS has a flexible architecture where each layer can be reused independently. It includes three layers as shown in the figure below, each based on an open standard. This complies with the general design principle of preservation systems to employ open standards wherever possible. At the top, the OAIS-based preservation engine layer provides an external interface to PDS and implements preservation functionalities. It includes efficient generation and placement of AIPs along with support for migration and data transformations performed within the storage. The second, optional layer is based on the eXtensible Access Method (XAM), a SNIA standard that provides logical abstraction for objects that include data and large amounts of metadata. The bottom layer of PDS (Object layer) is a backend storage system: a standard file system, or an Object-based Storage Device (OSD). A higher-level API (HL-OSD) on top of OSD provides abstraction and simplification to the Object Store’s SCSI-like interface. OSD is preferred when the actual disks are network-attached and there is a requirement to access them securely. This is an extension of the OSD (Object Storage Device) paradigm and standard previously developed by IBM Research – Haifa researchers.
Where the mid-layer abstraction is not desired, an alternative implementation maps the preservation engine layer directly to a file system object layer without using XAM.
Preservation DataStores Architecture