How to: EFS Basics
-	📒 [Homepage](https://aws.amazon.com/efs/) ∙ [User guide](http://docs.aws.amazon.com/efs/latest/ug) ∙ [FAQ](https://aws.amazon.com/efs/faq/) ∙ [Pricing](https://aws.amazon.com/efs/pricing/)
-	🐥**EFS** is Amazon’s network filesystem. It’s presented as an [NFSv4.1](https://en.wikipedia.org/wiki/Network_File_System#NFSv4) server. Any compatible NFSv4 client can mount it.
-	It is designed to be highly available and durable and each EFS file system object is redundantly stored across multiple availability zones.
-	EFS is designed to be used as a shared network drive and it can automatically scale up to petabytes of stored data and thousands of instances attached to it.
-	EFS can offer [higher throughput](http://docs.aws.amazon.com/efs/latest/ug/performance.html) (multiple gigabytes per second) and better durability and availability than EBS (see [the comparison table](#storage-durability-availability-and-price)), but with higher latency.
-	EFS is priced based on the volume of data stored, and costs [much more than EBS](#storage-durability-availability-and-price); it's in the ballpark of three times as much compared to general purpose gp2 EBS volumes.
-	⏱ [Performance](http://docs.aws.amazon.com/efs/latest/ug/performance.html) is dependent on the volume of data stored, as is the price:
	-	Like EBS, EFS uses a credit based system. Credits are earned at a rate of 50 KiB/s per GiB of storage and consumed in bursts during reading/writing files or metadata. Unlike EBS, operations on metadata (file size, owner, date, etc.) also consume credits. The [BurstCreditBalance metric](http://docs.aws.amazon.com/efs/latest/ug/monitoring-cloudwatch.html#efs-metrics) in CloudWatch should be monitored to make sure the file system doesn't run out of credits.
	-	Throughput capacity during bursts is also dependent on size. Under 1 TiB, throughput can go up to 100 MiB/s. Above that, 100 MiB/s is added for each stored TiB. For instance, a file system storing 5 TiB would be able to burst at a rate of 500 MiB/s. Maximum throughput per EC2 instance is 250 MiB/s.
	-	EFS has two performance modes that can only be set when a file system is created. One is "General Purpose", the other is "Max I/O". Max I/O scales higher, but at the cost of higher latency. When in doubt, use General Purpose, which is also the default. If the [PercentIOLimit metric](http://docs.aws.amazon.com/efs/latest/ug/monitoring-cloudwatch.html#efs-metrics) in CloudWatch hovers around 100%, Max I/O is recommended. Changing performance mode means creating a new EFS and migrating data.
-	High availability is achieved by having [mount targets in different subnets / availability zones](http://docs.aws.amazon.com/efs/latest/ug/images/overview-flow.png).

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