Transcript Drafting Behind Akamai (Travelocity
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 A lot of research in parallel I/O CPU power consumption grows super-linearly with speed.
They focus on workloads that are I/O, not computation, intensive.
Dynamic power scaling on traditional systems is surprisingly inefficient Electric cars consumes less power, but why you don’t buy it?
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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)
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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)
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.**
* http://www.genomeweb.com/informatics/no-flash-pan **
RETHINKING FLASH IN THE DATA CENTER
Flash Problems (Size)
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
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RETHINKING FLASH IN THE DATA CENTER
Flash Problems (translation layer)
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
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RETHINKING FLASH IN THE DATA CENTER
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.