Optimizing Magic Pocket for cold storage

When we first upload a file to Magic Pocket we use n-way replication across a relatively large number of storage nodes, but then later encode older data in a more efficient erasure coded format in the background. Magic Pocket stores blocks in a highly reliable manner within a storage region but it also stores this data independently in at least two separate regions. If we were to replicate data across regions instead of keeping a full internally-replicated copy in each region, we could reduce storage cost, but this would come with an increased wide-area network cost when we need to reconstruct a file during a region outage.

Source: blogs.dropbox.com