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What Is a Log-Structured File System?

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  • Written By: Alex Newth
  • Edited By: Angela B.
  • Last Modified Date: 23 November 2016
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A log-structured file system is a computer file system in which updating data is performed more quickly than in traditional methods, because most of the actions are made to be writes instead of seeks. Seeks often are performed by memory and file systems to find a file or coding, but a log-structured file system usually has very few seeks, because seeks tend to take a lot of time. Most file and archival memory systems available in 2011 prefer files with few seeks, because they pay much attention to where a file is located, so log-structured systems tend to work best with these systems. If the memory or file system accessing the log-structured system already has few seeks, then it may actually slow down the processing.

When a file system has to rewrite or change information, it normally does so by going to the individual datum and altering it. This system may sometimes be slow, and a log-structured file system uses a different approach to speed processing. Instead of adding this information directly to the file being changed, the log-structured system has a log to the side and all alterations are saved to the log. Newer edits are added on top, regardless of what program is being edited.

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When a file system needs to find a file or update, it uses a seek command that searches the entire system. While the seek command can be useful, especially for finding buried information, the command often takes a lot of time and memory. For this reason, the log-structured file system is built in a way that requires few seeks. This is mostly accomplished by the side log, because the seek can quickly search through the log rather than blindly searching the entire computer or server.

Most file and archival memory structures do not like using seeks, because these are only used when the system does not know where a file is located. When a log-structured file system is integrated with another system, such as an archival disk, the two usually work well together. This leads to quicker performance and saving between the log-structured system and the second system.

If the log-structured file system is integrated with another system that already has minimal seeks and does not perform many memory writes, then there can be a problem. Writes are not well supported, so the log-structured system’s heavy use of writes becomes a burden. The other system usually has to perform delete commands to make room for the new write, which takes a lot of time and memory to perform.

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