STEM Object Storage

STEM is a distributed storage cluster of immutable binary objects. STEM is based on top of Netty, Grizzly, Zookeeper and Cassandra (meta store). STEM has its own data storage format based on a bunch of pre-allocated blob containers called "fat files" of the same size.

STEM uses distribution strategy based on virtual partitioning (CRUSH implementation is used by default)

STEM is designed as a cheap solution for cloud hosting providers and can easily be deployed on commodity hardware. STEM does not need any vendor specific stuff like RAID or SAN, it uses plain formatted disks to store binary data.

With STEM each machine in cluster can store up to 100-200TB of data.

In terms of CAP theorem STEM is AP (high availability and partition tolerance) system.

STEM was inspired by Twitter Blobstore storage model

Features

Linear scalability
No single point of failure
High availability (x3 replication by default)
Heterogeneous design of cluster (binary objects are separated from meta data)
Linux/Windows compatible (HotSpot JVM)
Low cost — store up to 200TB of data on storage node
Stray forward compaction with no overhead (it takes few hours to free up space after deletion of data on a 3TB disk)
Automated cluster re-balancing logic — put into rack and power on
Process of data recover calculates dataset differences without overhead
Tolerate disk fragmentation by pre-allocating of disk space
True sequential write helps to reach the maximum capabilities of spindle disks
Tunable consistency on reads
Coordination and monitoring of data movement with Zookeeper
Uses Cassandra 2.0 as meta-data registry
Cluster management user interface
Hierarchical cluster topology
Data distribution logic is based on CRUSH algorithm to compute data flow
REST API (PUT, GET, DELETE)

Use cases

Linear scalability, high availability with zer-overhead compaction and repair make STEM perfect platform for the following production cases:

File storage backend, i.e. video hosting
Storage for a large amount of small blocks of data
Core engine for image hosting
Video hosting back-end

STEM Object Storage will allow you to install as many disks to storage node as you want. Indexes are located in a separate cluster; you don't need to worry about running out of RAM — meta- and binary- clusters can be scaled out separately.

Development

Intellij

Using If you're using Intellij, you need to install Lombok-Intellij https://code.google.com/p/lombok-intellij-plugin/
Import the project as a Maven Project.