One of the things people often ask about Perma.cc is how we ensure the preservation of Perma links. There are some answers in Perma's documentation, for example:

Perma.cc was built by Harvard’s Library Innovation Lab and is backed by the power of libraries. We’re both in the forever business: libraries already look after physical and digital materials — now we can do the same for links.

and:

How long will you keep my Perma.cc Links?

Links will be preserved as a part of the permanent collection of participating libraries. While we can't guarantee that these records will be preserved forever, we are hosted by university libraries that have endured for centuries, and we are planning to be around for the long term. If we ever do need to shut down, we have laid out a detailed contingency plan for preserving existing data.

The contingency plan is worth reading; I won't quote it here. (Here's a Perma link to it, in case we've updated it by the time you read this.) In any case, all three of these statements might be accused of a certain nonspecificity - not as who should say vagueness.

I think what people sometimes want to hear when they ask about preservation of Perma links is a very specific arrangement of technology. A technologically specific answer, however, can only be provisional at best. That said, here's what we do at present: Perma saves captures in the form of WARC files to an S3 bucket and serves them from there; within seconds of each capture, a server in Germany downloads a copy of the WARC; twenty-four hours after each capture, a copy of the WARC is uploaded to the Internet Archive (unless the link has been marked as private); also at the twenty-four hour mark, a copy is distributed to a private LOCKSS network. The database of links, users, registrars, and so on, in AWS, is snapshotted daily, and another snapshot of the database is dumped and saved by the server in Germany.

Here's why that answer can only be provisional: there is no digital storage technology whose lifespan approaches the centuries of acid-free paper or microfilm. Worse, the systems housing the technology will tend to become insecure on a timescale measured in days, weeks, or months, and, unattended, impossible to upgrade in perhaps a few years. Every part of the software stack, from the operating system to the programming language to its packages to your code, is obsolescing, or worse, as soon as it's deployed. The companies that build and host the hardware will decline and fall; the hardware itself will become unperformant, then unusable.

Mitigating these problems is a near-constant process of monitoring, planning, and upgrading, at all levels of the stack. Even if we were never to write another line of Perma code, we'd need to update Django and all the other Python packages it depends on (and a Perma with no new code would become less and less able to capture pages on the modern web); in exactly the same way, the preservation layers of Perma will never be static, and we wouldn't want them to be. In fact, their heterogeneity across time, as well as at a given moment, is a key feature.

The core of digital preservation is institutional commitment, and the means are people. They require dedication, expertise, and flexibility; the institution's commitment and its staff's dedication are constants, but their methods can't be. The resilience of a digital preservation program lies in their careful and constant attention, as in the commonplace, "The best fertilizer is the farmer's footprint."

Although I am not an expert in digital preservation, nor well-read in its literature, I'm a practitioner; I'm a librarian, a software developer, and a DevOps engineer. Whether or not you thought this was fertilizer, I'd love to hear from you. I'm bsteinberg@law.harvard.edu.