[Pasig-discuss] WORM (Write Once Read Many) AIPs

[Neil Jefferies]

Tim,

If we store AIP's unpackaged, as a collection of files in a folder, then 
object updates could just be a new folder with symlinks to the unchanged 
parts and the updated parts in place in the folder. The object 
"location" would be a parent folder for all these version folders - for 
example, a pairtree (or triple-tree for faster scanning/rebuilds) based 
on object UUID. Version folders would be named accoprding to date or 
version number (date might make Memento compliant access simpler). 
Creating anew version clones the current verion (including links) with a 
new name and then replaces the updated parts in situ. Final act is to 
update a "current" symlink in the object. Any update failure will mean 
"current" is not updated an the partial clone can be discarded.

This assumes most updates are metadata and that a diff won't save much 
compared to a complete new XML file or whatever. I am also assuming that 
metadata won't be wrappered either (so you can forget METS) so that 
different types are stored in the most stuiable format and are accessed 
only when required. The problems with roundtripping packaged AIP's for 
updates rather than diff-ing are repeated by METS wrappering.

These may be a virtual folder/filesytem presentation and underneath an 
HSM would retrieve files from wherever when it is actually accessed. HSM 
policy in soemthing like SAM-QFS/Versity/Cray TAS can ensure folders are 
kep intact when moved to other storage (we could even dereference 
symlinks when dealing with tape).

This can be done with a POSIX filesystem and not muich code - Ben 
O'Steen started something along these lines here: 
https://github.com/dataflow/RDFDatabank/wiki/What-is-DataBank-and-what-does-it-do%3F

Fedora also also a versioning object store that could support this kind 
of model but also adds a fair bit of complexity to be 
Linked-Data_platform compliant.

In my paralance I would probably equate "Minimal Ingest" with "Sheer 
Curation" and APT with Asynchronous Message Driven Workers.

Neil


On 2017-05-12 12:33, Tim.Gollins at nrscotland.gov.uk wrote:
> Dear PASIG
> 
> I have been thinking recently about the challenge of managing
> "physical"  AIPs on offline or near line storage and how to optimise
> or simplify the use of managed storage media in a tape based (robotic)
> Hierarchical Storage Management (HSM) system. By "physical" AIPs I
> mean that the actual structure of the AIP written to the storage
> system is sufficiently self-describing that even if the management or
> other elements of a DP system were to be lost to a disaster then the
> entire collection could be fully re-instated reliably from the stored
> AIPs alone.
> 
> I have also been thinking about the huge benefits of adopting the
> concepts of "Minimal Ingest" (MI) and "Autonomous Preservation Tools"
> (APT) in a new Digital Archive solution.
> 
> One of the potential effects of the MI and APT concepts is that over
> time it is clear that while (of course) the original bit streams will
> never need to be updated, the metadata packaged in the AIP will need
> to change relatively often (through the life of the AIP) . This is of
> course in addition to any new renderings of the bit streams produced
> for preservation purposes (manifestations as termed in some systems).
> 
> If to update the AIP the process involves the AIP being "loaded" and
> "Modified" and "Stored" again as a whole then this will result in
> significant "churn" of the offline or near line media (i.e. tapes) in
> a HSM - which I would like to avoid. I think it would be really great
> if the AIP representation could accommodate the concept of an "update
> IP" (perhaps UIP?) where the UIP contains a "delta" of the original
> AIP - the full AIP then being interpreted as the original as modified
> by a series of deltas. This would then effectively result in AIPs (and
> UIPs) becoming WORM objects with clear benefits that I perceive in
> managing their reliable and safe storage.
> 
> I am not sufficiently familiar with the detail of all the different
> AIP models or implementations, I was wondering if anyone in the team
> would be able to comment on whether the they know of any AIP models,
> specifications or implementations that  would support such a use case.
> 
> I have just posted a version of this question to the E-Ark Linked in
> Group so my apologies to those who see it twice.
> 
> Many thanks
> 
> Tim
> Tim Gollins | Head of Digital Archiving and Director of the NRS
> Digital Preservation Programme
> National Records of Scotland | West Register House | Edinburgh EH2 4DF
> + 44 (0)131 535 1431 / + 44 (0)7974 922614 |
> tim.gollins at nrscotland.gov.uk | www.nrscotland.gov.uk
> 
> Preserving the past | Recording the present | Informing the future
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