delphij's Chaos


18 Jan 2004



tjr写道: “Initial work on a new filesystem. Right now we can mount it, list
directories, and copy small files off it, but there is no write
support yet. This is going to be a simple extent-based filesystem,
borrowing ideas from NTFS and EFS.”



An extent is defined as one or more adjacent blocks of data within the filesystem. When storage is added to a file on a vxfs filesystem, it is grouped in extents, as opposed to being allocated a block at a time (as is done by the s5, sfs, and ufs filesystems).

Using extents means that disk I/O to and from a file can be done in units of multiple blocks. This type of I/O can occur if storage is allocated in units of consecutive blocks. For sequential I/O, multiple block operations are considerably faster than block-at-a-time operations. Almost all disk drives accept I/O operations of multiple blocks.