Softupdates

Under Soft Updates is meant an extension to the UNIX File System ( UFS), which has two main objectives:

• Guarantee the consistency of the file system metadata without journaling
• To keep losses in the write speed of this measure as low as possible

This functionality is achieved in that all blocks to be written, metadata, such as for an entire list held in the RAM, processed, and sorted in a specific order to the medium (e.g. disk) is written.

As an effect, it looks like a unscheduled reboot, for example due to power failure or system crash, basically like this, as if writing the metadata either completely or not at all taken place on the hard drive, in other words, meta- updates are atomic ( indivisible ). The file system is always in a consistent state. The only possible error that may appear in this process, are blocks in the file system that are still marked as busy, even though they should already be free. For this reason, check the file system on its block assignment is necessary.

Under the FreeBSD operating system from version 5.x, however, it is possible, in contrast to previous implementations, to let this file system check ( fsck ) running in the background. Thus, the time is considerably reduced to boot the system with a very large file systems.

In practice, software updates work most reliably when the write cache of the hard disk is turned off, which in most hard disks sensitive performance degradation has. This property share Soft Updates and journaling.

The extension Soft Updates for UFS is currently available in two of the BSD variants:

• OpenBSD 2.3 ( November 1997) and newer versions
• FreeBSD 4.0 ( March 1998) and newer versions