Erasure code saves storage space and increases durability. Most commonly used in its simplest form (RAID5), erasure code is generalized for networked storage. It was first introduced in Ceph with the Firefly release in 2014. In this session, we’ll explain, with a lively experiment, the erasure code logic. We’ll give you an overview of the Ceph implementation and its most common use cases and go on to explain the various erasure code plug-ins (jerasure, ISA-L, LRC). Finally, we’ll show you how to estimate the trade off between erasure coding and replication—a choice that comes down to space versus speed.

1. Erasure Code in Ceph
Loic Dachary @ Red Hat

2. Save Space

3. 5 minutes role playing game

4. XOR

5. 3 peta => 1.3 peta

6. Harder object mutations / recovery

7. Simple operations and tiering
Replicated Erasure Coded

8. Promoted to replica on read
Replicated Erasure Coded

9. Sam & David : internals

10. Janne & Andreas & Loic & Takeshi
erasure code

11. Released May 2014 : Firefly

12. Why save space before shortage ?

13. Reliability Model
● After an OSD is lost
● Recovery
● Backfilling a new OSD

14. April 2015 : Hammer

15. Repair K=10, M=4

16. Locally Recoverable Codes
LRC @ Red Hat

17. SHEC Takeshi @ Fujitsu

18. ISA plugin Yuan @ Intel
SIMD aka SSE2, SSE3, SSE4
Only for Intel processors
~50% Faster

19. jerasure ARM Janne @ ARM

20. Infernalis

21. Hitchhiker Rashmi @ U.C. Berkeley

22. ldachary@redhat.com
Artwork GPLv3+ Tartaruga Feliz