our company wants to backup 500 TB to AWS S3 Glacier and I was wondering if anyone has done such a thing already with restic.
One interesting question is if it needs to read back data later (and how much) to create increments or if it keeps sufficient local data about chunk hashes.
The other interesting question then is how a restore operation would work (as disaster recovery only) with such a slow archive.
First, restic currently does not officially support cold storages - it is designed to have instant access to the storage backend.
Moreover there are quite some discussions if AWS Glacier is really a cheap storage for backups as the retrieve costs are probably too high to profit from the low storage costs. But for a desaster-recovery maybe this could be still an option.
I’m trying to make some proposals which would allow restic to work with cold storages, see
Now, about your questions:
Basically, restic needs to regularly access its metadata to run and speed up backups, checks, etc. Metadata is everything except the file contents which are saved within restic in so called “data pack files”. See the link above about which restic functionality works with accessing only metadata.
So the goal is to split your repo such that the metadata is always available (“hot”) and the data pack files are saved in some “cold” storage, in your case S3 Glacier.
With AWS, you can specify the storage class by the path in the repo (e.g. save everything under /data/ in Glacier and use S3 Standard for all other paths in your repo. The bad thing is, that under /data/ all data pack files are saved as well as all tree pack files (which are metadata and frequently used).
So, you have basically two options:
Or you you just save everything under /data/ in S3 Glacier and rely on the local cache restic creates and uses to access all tree pack files.
This also means, if you loose your local cache, things will get ugly to recreate that cache, but the way would be to identify your tree pack files, warm them up and run your backups to re-create the cache.