Originally Published: Monday, 16 August 1999 Author: Scott Nipp
Published to: featured_articles/Featured Articles Page: 1/1 - [Printable]

XFS - What it means for Linux

What is the reason for all the hype surrounding SGI releasing XFS under the GPL? This is a question that a lot of people seem to be asking these days. Another is, "What is the big deal about a journalling filesystem, and how will it help me?" These are the questions I will attempt to answer....

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What is the reason for all the hype surrounding SGI releasing XFS under the GPL? This is a question that a lot of people seem to be asking these days. Another is, "What is the big deal about a journalling filesystem, and how will it help me?" These are the questions I will attempt to answer.

XFS is a "journalling" filesystem which SGI originally developed for their IRIX platform. A journalling filesystem is one which logs the activity of the filesystem, thus making crash recovery much quicker. This log means that in the event of a power failure, the filesystem has a record as to what it was doing when the failure occurred. This means that the filesystem does not have to go through a lengthy consistency check--fsck in Linux terms. Journalling functions basically as follows: when a file write operation is to occur, the filesystem first writes what is called an intent-to-change record to the filesystem log, or journal. Next, the actual file write operation is accomplished. Finally, the log entry is marked complete and then deleted. This eliminates the need to check the entire filesystem in the event of a failure. Instead of checking the entire filesystem, the system simply checks the log, and if an intent-to-change entry is found not marked complete, then the file structure for that block is checked and adjusted where necessary.

XFS also has several other benefits to offer the Linux community. XFS is a 64-bit filesystem, which means that it can support ridiculously large files (9 million terabytes), and even larger filesystems (18 million terabytes). To understate how much space this is, it is phenomenal. XFS delivers all this capacity and reliability with amazing speed. XFS is also compatible with other popular services including various backup solutions, and file sharing via NFS or Samba.

This brings us to the issue of how this benefits the Linux world. The performance and flexibility of XFS is reason enough to make it an asset to the Linux community, but journalling makes it a gold mine. Corporations which have huge databases and other electronic data cannot afford the downtime it would take for a complete filesystem check on a large filesystem. I think we are all familiar with how long an fsck takes on our 4GB or 8GB drives. Imagine how long that fsck would take on a 200GB filesystem--or better yet, a 1TB filesystem. A complete filesystem check on a volume like this could take hours. This is time that large corporations just can't afford to lose.

A journalling filesystem for Linux will be one less weakness. This technology will help to further the penetration which Linux has already obtained into the corporate server rooms. This type of filesystem, along with the recent releases of major databases by companies such as Oracle, Informix and Sybase, will help to propel Linux into the database server role. This will in affect give doubting IT managers one less argument to use against the idea of bringing Linux into their organization.

Scott Nipp works as a Technical Analyst at Sprint Paranet. He spends his time fighting the good fight, advocating Linux to his managers and customers.





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