Archiving data in glass

Most digital storage mediums age worse than paper, and certainly worse than words carved into stone. Tapes last a decade or two. Hard disks and SSDs less time still — you need to replace them about every five years if you want to be confident in not losing something along the way. So how do we keep digital data for a long time — hundreds or thousands of years?

Microsoft’s Project Silica is one attempt to answer this question.

Silica aims to be a complete storage system using a very stable storage substrate — quartz glass. It writes data by altering the structure of glass platters with a powerful laser. You can write it just the once. It’s read using far less powerful light beams, meaning that reading doesn’t degrade the stored data.

Ultrafast femtosecond lasers enable the writing process. Data is written inside a square glass platter similar in size to a DVD through voxels, permanent modifications to the physical structure of the glass made using femtosecond-scale laser pulses. Voxels encode multiple bits of data and are written in 2D layers across the XY plane. Hundreds of these layers are then stacked in the Z axis.

The project has been designed around the idea that it might be used as an archival tier in a cloud storage solution — not just for archiving data deemed “important” enough to keep, but anyone’s data. After all, some of the most interesting texts we find in archaeology are leftover everyday notes or diaries that tell us scraps of everyday life. (Like Sumerian tablets tracking trades of pig fat from 4,200 years ago).

For a cloud service, as well as writing and reading, you need to be able to delete it, even if you can’t update it. Deleting data is handled using crypto-erasure — all the data is encrypted, and to delete you destroy the relevant keys. If all the data on a platter is erased, you can melt down the platter and create a new one ready to use. Presumably future archaeologists with fancy quantum computers will be able to decrypt this data when they dig it up 🙃

Each platter is a small rectangle of glass, rather like a microscope slide. Using the layered-writing approach each platter can store a few TB of data. How do you store and access all these bits of glass? Why, you build some super-cool robots that can slide along and climb between your shelves of glass platters, of course!

I love the technologies involved in this. But, more I love the fact that the research is creating a media that’s stable for thousands of years, and can retain data without needing to periodically refresh it or keep it in atmospherically-controlled vaults. This means that the data can live beyond the lifespan of our civilisation, both because of the stability of the storage medium itself, but also because it doesn’t need us around to prevent it degrading. Like those tablets about pig fat. Which is really rather cool.

Here’s the full paper: Project Silica: Towards Sustainable Cloud Archival Storage in Glass - Microsoft Research.