Concurrent Big Data applications often require high-performance storage, as well as ACID (Atomicity, Consistency , Isolation, Durability) transaction support. Although blobs (binary large objects) are an increasingly popular model for addressing the storage needs of such applications, state-of-the-art blob storage systems typically offer no transaction semantics. This demands users to coordinate access to data carefully in order to avoid race conditions, inconsistent writes, overwrites and other problems that cause erratic behavior. We argue there is a gap between existing storage solutions and application requirements, which limits the design of transaction-oriented applications. We introduce Tyr , the first blob storage system to provide built-in, multiblob transactions, while retaining sequential consistency and high throughput under heavy access concurrency. Tyr offers fine-grained random write access to data and in-place atomic operations. Large-scale experiments on Microsoft Azure with a production application from CERN LHC show Tyr throughput outperforming state-of-the-art solutions by more than 75%.