US 5,819,292 A · Method for maintaining consistent states of a file system and for creating user-accessible read-only copies of a file system

Abstract

A method is disclosed for maintaining consistent states of a file system. The file system progresses from one self-consistent state to another self-consistent state. The set of self-consistent blocks on disk that is rooted by a root inode is referred to as a consistency point. The root inode is stored in a file system information structure. To implement consistency points, new data is written to unallocated blocks on disk. A new consistency point occurs when the file system information structure is updated by writing a new root inode into it. Thus, as long as the root inode is not updated, the state of the file system represented on disk does not change. The method also creates snapshots that are user-accessible read-only copies of the file system. A snapshot uses no disk space when it is initially created. It is designed so that many different snapshots can be created for the same file system. Unlike prior art file systems that create a done by duplicating an entire inode file and all indirect blocks, the method of the present invention duplicates only the inode that describes the inode file. A multi-bit free-block map file is used to prevent data referenced by snapshots from being overwritten on disk.

Claims20

Dependent claims

A method for recording a plurality of data about a plurality of blocks of data stored in storage means comprising the steps of:

maintaining a means for recording multiple usage bits per block of said storage means, wherein one bit of said multiple bits per block for each of said blocks indicates a block's membership in an active file system and one or more bits indicated membership in one or more read-only copies of a file system;
and
storing in said means for recording multiple usage bits per block multiple bits for each of a plurality of said blocks of said storage means.

A method for maintaining a file system stored in non-volatile storage means at successive consistency points said file system comprising blocks of data, said blocks of data comprising blocks of regular file data and blocks of meta-data file data referencing said blocks of data of said file system, said meta file data comprising a file system information structure comprising data describing said file system at a first consistency point said computer system further comprising memory means, said method comprising the steps of:

maintaining a plurality of modified blocks of regular file data and meta-data file data in said memory means, said modified blocks of data comprising blocks of data modified from said first consistency point;
designating as dirty blocks of meta-data file data referencing said modified blocks of regular file data and meta-data file data, said dirty blocks of meta-data file data comprising blocks of meta-data file data to be included in a second consistency point;
copying said modified blocks of regular file data referenced by said dirty blocks of meta-data file data to free blocks of said non-volatile storage means;
copying blocks comprising said modified blocks of meta-data file data referenced by said dirty blocks of meta-data file data to free blocks of said non-volatile storage means;
modifying a copy of said file system information structure maintained in said memory means to reference said dirty blocks of meta-data file data:
copying said modified file system information structure to said non-volatile storage means.

3 more elements

A method for maintaining a file system comprising blocks of data stored in blocks of a non-volatile storage means at successive consistency points comprising the steps of:

storing a first file system information structure for a first consistency point in said non-volatile storage means, said first file system information structure comprising data describing a layout of said file system at said first consistency point of said file system;
writing blocks of data of said file system that have been modified from said first consistency point as of the commencement of a second consistency point to free blocks of said non-volatile storage means;
storing in said non-volatile storage means a second file system information structure for said second consistency point, said second file system information structure comprising data describing a layout said file system at said second consistency point of said file system.

Dependencies are inferred from the claim text.

Method for maintaining consistent states of a file system and for creating user-accessible read-only copies of a file system

Life of this patent

Method for maintaining consistent states of a file system and for creating user-accessible read-only copies of a file system

Life of this patent

Abstract

Claims20