Dropbox Tech

Improving Storage Efficiency in Magic Pocket, Our Immutable Blob Store

Dropbox’s exabyte‑scale immutable blob store, Magic Pocket, faced a sharp rise in storage overhead after a new Live Coder service created many under‑filled volumes. To combat the fragmentation, the engineering team introduced two additional compaction strategies—L2, a dynamic‑programming‑based volume packer, and L3, a streaming pipeline that drains the sparsest volumes. Together with a dynamic eligibility‑threshold control loop, the three‑tiered approach reduced overhead 30‑50% within days and restored efficiency below the pre‑incident baseline. The changes also tightened monitoring to catch future distribution shifts early.