POHMELFS is an asynchronous cache coherent

Cache coherence

In computing, cache coherence refers to the consistency of data stored in local caches of a shared resource.When clients in a system maintain caches of a common memory resource, problems may arise with inconsistent data. This is particularly true of CPUs in a multiprocessing system...

 distributed file system

Distributed file system

Network file system may refer to:* A distributed file system, which is accessed over a computer network* Network File System , a specific brand of distributed file system...

 developed by Russia

Russia

Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

n Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

 hacker Evgeniy Polyakov. The current implementation could be seen as a smart and fast replacement of the widely used Network File System (NFS) protocol (which is used to share filesystems between networked computers), with the possibility to use parallelized connections to speed up the transfers. The design roadmap plans to converge it towards a true distributed file system with good scalability, strong fault tolerance and caching.

It was announced on January 31, 2008, and merged into the mainline Linux kernel

Linux kernel

The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software....

 version 2.6.30, released June 9, 2009. It is named after the Russian похмелье (pohmel'e) meaning "hangover

Hangover

A hangover describes the sum of unpleasant physiological effects following heavy consumption of alcoholic beverages. The most commonly reported characteristics of a hangover include headache, nausea, sensitivity to light and noise, lethargy, dysphoria, diarrhea and thirst, typically after the...

".

Features

Key features include local caching of data and metadata, asynchronous processing of almost all events, dynamic (on-line) reconfiguration, full transactions with failover to alternate servers, parallel writes to multiple servers, and strong authentication

Authentication

Authentication is the act of confirming the truth of an attribute of a datum or entity...

 and encryption

Encryption

In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...

. The server runs in user space

User space

A conventional computer operating system usually segregates virtual memory into kernel space and user space. Kernel space is strictly reserved for running the kernel, kernel extensions, and most device drivers...

, and high performance is one of the key design goals.

Roadmap

The main feature still waiting to be implemented is to convert POHMELFS to use the Elliptics network project (fault-tolerant distributed hash table object storage) and the Distributed network storage (DST) project, and thus support a fully distributed file system. Another feature on the waiting list is data channel compression between nodes.

History

The file system design started around November, 2007.

PohmelFS (as in the original spelling) was born on the date Mon Dec 10 19:38:53 MSK 2007 (Moscow time), and has been released to the public on 31 January, 2008.

In November, 2008 it's been announced that the file system is going to be redesigned to be a true distributed file system by using the author's new mature projects: DST (Distributed network storage) and the Elliptics network, a fault-tolerant distributed hash table

Distributed hash table

A distributed hash table is a class of a decentralized distributed system that provides a lookup service similar to a hash table; pairs are stored in a DHT, and any participating node can efficiently retrieve the value associated with a given key...

 object storage. The result should be a distributed, parallel file system with distributed locking, cache coherency and fault tolerance.

See also

• List of file systems, distributed file systems section
• Comparison of file systems
  Comparison of file systems
  -General information:-Limits:-Metadata:-Features:-Allocation and layout policies:-Supporting operating systems:-See also:* Comparison of archive formats* Comparison of file archivers* List of archive formats* List of file archivers...
  
  
• Network File System (protocol)

External links

• POHMELFS homepage
• Linux 2.6.30: POHMELFS and DST at Kernel Newbies
• POHMELFS performance and full transaction support at Kernel Trap
• CRFS and POHMELFS at Linux Weekly News