FAWN: A Fast Array of Wimpy Nodes Authors: David G. Andersen et al. Offence: Jaime Espinosa Chunjing Xiao
Why FAWN Not • Increasing CPU-I/O Gap • CPU power consumption grows super-linearly with speed. • Dynamic power scaling on traditional systems is surprisingly inefficient • A lot of research in parallel I/O • They focus on workloads that are I/O, not computation, intensive. • Electric cars consumes less power, but why you don’t buy it?
Poor scaling characteristics • The system includes a number of relatively high powered front-end systems • Analysis has shown that for data-intensive workloads, large wimpy node clusters suffer from poor scaleup effects, • Because they are more affected by a diminishing return scaleup effect than a smaller traditional cluster* *Wimpy Node Clusters: What About Non-Wimpy Workloads (3.5.4 Discussion) 3
Limitations(1) Only focus on read-mostly workloads (simple key-value workloads). They can not provide complex processing workload and it is bad for write-most workloads. 4
Limitations(2) Works only for small data and small CPU work-loads Conclusions from author: not going to replace current data-center, does not work for real-time applications (ie. gaming) Does not have ACID property that is desired in data bases (Atomicity Consistency Isolation Durability) 5
Reliability problems • More nodes & hardware components leads to more failures • less memory per node than traditional systems • conversely more nodes are required for the same capacity. • Communication, link and switch failure not considered
Flash Problems (cost) *http://www.genomeweb.com/informatics/no-flash-pan **RETHINKING FLASHIN THE DATA CENTER • Why did they only examine 3-year total cost of ownership (TCO) in Section 5? • flash storage has short lifetime • Flash is 15-20 times more expensive than HDD.* • the smaller flash cells are less reliable and less durable.**
Flash Problems (Size) *RETHINKING FLASHIN THE DATA CENTER • The amount of physical space per megabyte is a problem • Thermodynamically requires more energy • It takes longer to heat a large room than a small one • Environmental foot-print is relative to area needed
Flash Problems (translation layer) *RETHINKING FLASHIN THE DATA CENTER • Through heroic engineering and daunting complexity, the flash translation layer masks these problems, but its performance impact can be significant. • Intel’s Extreme SSDs have a read latency of 85 ms, but the flash chips the drive uses internally have a read latency of just 25 to 35 ms.* • Flash translation layer is part of the flash controller and is embedded in flash chips and drives
Race Conditions • Another study* from CMU found that the system leads to race conditions *dBug: Systematic evaluation of Distributed Systems
Conclusion It is a great system for quickly finding tiny amounts of data provided you have a lot of real-estate and don’t mind the high probability of failure.