Next3 is a

journaling file system A journaling file system is a file system that keeps track of changes not yet committed to the file system's main part by recording the goal of such changes in a data structure known as a " journal", which is usually a circular log. In the even ...

for

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...

based on

ext3 ext3, or third extended filesystem, is a journaled file system that is commonly used by the Linux kernel. It used to be the default file system for many popular Linux distributions. Stephen Tweedie first revealed that he was working on ext ...

which adds

snapshots Snapshot, snapshots or snap shot may refer to: * Snapshot (photography), a photograph taken without preparation Computing * Snapshot (computer storage), the state of a system at a particular point in time * Snapshot (file format) or SNP, a file ...

support, yet retains compatibility to the ext3 on-disk format. Next3 is implemented as

open-source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product. The open-source model is a decentralized so ...

software, licensed under the GPL license.

Background

A snapshot is a read-only copy of the file system frozen at a point in time. Versioning file systems like Next3 can internally track old versions of files and make snapshots available through a special

namespace In computing, a namespace is a set of signs (''names'') that are used to identify and refer to objects of various kinds. A namespace ensures that all of a given set of objects have unique names so that they can be easily identified. Namespaces ...

Features

Snapshots

An advantage of

copy-on-write Copy-on-write (COW), sometimes referred to as implicit sharing or shadowing, is a resource-management technique used in computer programming to efficiently implement a "duplicate" or "copy" operation on modifiable resources. If a resource is dupl ...

is that when Next3 writes new data, the blocks containing the old data can be retained, allowing a snapshot version of the file system to be maintained. Next3 snapshots are created quickly, since all the data composing the snapshot is already stored; they are also space efficient, since any unchanged data is shared among the file system and its snapshots.

Dynamically Provisioned Snapshots Space

The traditional Linux

Logical Volume Manager In computer storage, logical volume management or LVM provides a method of allocating space on mass-storage devices that is more flexible than conventional partitioning schemes to store volumes. In particular, a volume manager can concatenate ...

volume level snapshots implementation requires that storage space be allocated in advance. Next3 uses Dynamically provisioned snapshots, meaning it does not require pre-allocation of storage space for snapshots, instead allocating space as it is needed. Storage space is conserved by sharing unchanged data among the file system and its snapshots.

Compatibility

Since Next3 aims to be both forward and

backward compatible Backward compatibility (sometimes known as backwards compatibility) is a property of an operating system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially in ...

with the earlier ext3, all of the on-disk structures are identical to those of ext3. The file system can be mounted for read by existing ext3 implementations with no modification. Because of that, Next3, like ext3, lacks a number of features of more recent designs, such as extents.

Performance

When there are no snapshots, Next3 performance is equivalent to ext3 performance. With snapshots, there is a minor overhead per write of metadata block (copy-on-write) and a smaller overhead (~1%) per write of data block (move-on-write).

Next4

As of 2011, Next4, a project for porting of Next3 snapshot capabilities to the

Ext4 ext4 (fourth extended filesystem) is a journaling file system for Linux, developed as the successor to ext3. ext4 was initially a series of backward-compatible extensions to ext3, many of them originally developed by Cluster File Systems for ...

file system, is mostly completed. The porting is attributed to members of the Pune Institute of Computer Technology (PICT) and the

Chinese Academy of Sciences The Chinese Academy of Sciences (CAS); ), known by Academia Sinica in English until the 1980s, is the national academy of the People's Republic of China for natural sciences. It has historical origins in the Academia Sinica during the Republi ...

.NEXT3 Filesystem Home Page
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References

{{File systems Disk file systems File systems supported by the Linux kernel 2010 software Computer file systems