Carlos, you are mistaken re: Haystack. I don't think it was ever planned to be replaced, it's always been in use as a hot blob storage engine since it was launc

Carlos, you are mistaken re: Haystack. I don't think it was ever planned to be replaced, it's always been in use as a hot blob storage engine since it was launched. There are three storage layers for blobs at Facebook: hot (Haystack @ 3.6x replication), warm (F4 @ 2.1x), cold (Cold Storage @ 1.4x). We have published papers describing each layer. Haystack still handles the initial writes and the burst of heavy read traffic when an object is fresh. It has a higher space overhead of 3.6x because it's optimized for throughput and latency versus cost savings. The Haystack tier's size is now dwarfed by the size of the F4 and Cold Storage tiers, but it still handles almost all of the reads for user blobs on Facebook due to the age/demand exponential curve. After a haystack volume is locked and has cooled down enough, it moves to F4 to bump its replication factor way down for cheaper, longer term online storage. And then Cold Storage is used for the older stuff that gets barely any reads but that you still want to store online for perpetuity. That is why the team that works on media storage is called Everstore; they take storing people's photos and videos seriously and view it as a promise to keep your memories available forever. It feels really good to see photos from 5+ years ago and have them still work, and someday there will be 30 year old photos and videos on Everstore as well. Source: I built Haystack with a couple other people and founded the Everstore team. :-)