1. If the server is used as a web service that provides a static file, open SoftUpdate and does not have much impact on disk performance?
SoftUpdates only optimizes the performance of the write metadata, so I think that it should not be opened. 2, if Database application, performance is greatly improved, the risk is very high?
If your database server is written (ie, each CommIT operation is fsync), there will be no effect. Some irresponsible operating system / file system / database systems are not synchronous, but FreeBSD is (this is also a lot of evaluation reports claiming freebsd slower because some other OS is an ASYNC mount).
The performance improvement is high depending on the nature of your database application. In general, although SoftUpdates will have some improvements, it will not be obvious, because typical database programs do not often lead to metadata update operations for file systems (A.K.A. Trunc, Creat, Unlink, etc.). The normal database system developers are usually pre-allocated, including logs and data itself, SoftUpdates can accelerate substantially limited to this. Of course, if you don't do this, you may have a big improvement. 3. Even if you open SoftUpdate, you will not cause the system to crash, only the data is lost?
For IDE hard drives, you must turn off the IDE write cache (the log system is also the same, but many implementations do not do this). The method is to add hw.ata.wc = "0" in /boot/loader.conf. This option significantly reduces the write performance of the disk, but is critical to keeping data consistency.
SCSI hard drives do not have such problems (they usually support tagged queue, and will not ly on the operating system)
If you are confident that the disk does not deceive the operating system (for example, it is just in cache, it has been written, the method is to disable the IDE write cache, or enable SCSI's tagged Queue capability), you can determine that SoftUpdates can not be discharged. Damage FS, you lose only to write or create file data for the last 30 seconds, and a small amount of disk space. For FreeBSD 5.x, these spaces can be recycled after the system is started after the system is started, which greatly reduces the time required to start.
