git-annex/doc/todo/S3.mdwn
2011-03-18 09:47:12 -04:00

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Support Amazon S3 as a file storage backend.
There's a haskell library that looks good. Not yet in Debian.
Multiple ways of using S3 are possible. Current plan is to have a S3BUCKET
backend, that is derived from Backend.File, so it caches files locally and
can transfer files between systems too, without involving S3.
get will try to get it from S3 or from a remote. A annex.s3.cost can
configure the cost of S3 vs the cost of other remotes.
add will always upload a copy to S3.
Each file in the S3 bucket is assumed to be in the annex. So unused
will show files in the bucket that nothing points to, and dropunused remove
them.
For numcopies counting, S3 will count as 1 copy (or maybe more?), so if
numcopies=2, then you don't fully trust S3 and request git-annex assure
one other copy.
drop will remove a file locally, but keep it in S3. drop --force *might*
remove it from S3. TBD.
annex.s3.bucket would configure the bucket the use. (And an env var or
something configure the password.) Although the bucket
would also be encoded in the keys. So, the configured bucket would be used
when adding new files. A system could move from one bucket to another over
time while still having legacy files in an earlier one;
perhaps you move to Europe and want new files to be put in that region.
And git annex `migrate --backend=S3BUCKET --force` could move files
between datacenters!
Problem: Then the only way for unused to know what buckets are in use
is to see what keys point to them -- but if the last file from a bucket is
deleted, it would then not be able to say that the files in that bucket are
all unused. Need cached list of recently seen S3 buckets?
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One problem with this is what key metadata to include. Should it be like
WORM? Or like SHA1? Or just a new unique identifier for each file? It might
be worth having S3 variants of *all* the Backend.File derived backends.
More blue-sky, it might be nice to be able to union or stack together
multiple backends, so S3BUCKET+SHA1 or S3BUCKET+WORM. That would likely
be hard to get right.
Less blue-sky, if the S3 capability were added directly to Backend.File,
and bucket name was configured by annex.s3.bucket, then any existing
annexed file could be upgraded to also store on S3.