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Chapter 6There are actually four different modes that you can use to mount a UFS file system:• Sync: In this mode all I/O to file will be done synchronously. This meansthat both data and metadata will be written synchronously to the disk.Although this will slow down the disk I/O performance, this makes thesystem immune to crashes.• Noasync: In this mode, data is written to disk asynchronously while metadatais written synchronously. This will greatly enhance performance, ascompared to the sync mode, and is also almost safe from system crashes.• Softupdates: This method properly orders the metadata writes and ensuresconsistency of data on disk. The performance in this mode is somewhat likenoasync mode. This feature has been explained in Chapter 1.• Async: This is the fastest, but the most dangerous method. All writes in thismode are done asynchronously and there is a high risk of data loss in case ofpower failure.Noasync is the default mode, if nothing else is specified.Modes can be set by using mount(8)'s -o option . You should also update the"options" column in the /etc/fstab file, for the changes take effect upon a systemboot up.Do not use async mode for root partition. Corrupting of this partition mayprevent your system from booting up correctly.By default, the system updates the last access time of any file that is being accessed.This will produce I/O overhead on the busy file systems. If you do not want toknow when a file was accessed the last time, you may want to turn this feature off, toimprove the disk I/O performance. To turn this feature off, you should set the noatimeoption on any partition. During run time, you must use the following command:# mount –u –o noatime /usrThis will turn the noatime flag on, on the /usr partition. To make these changespermanent, the /etc/fstab file must be updated accordingly.RAIDRAID (explained in Chapter 1, System Configuration—Disks), will also help youreduce I/O overheads and improve the disk read/write times. You should selecta RAID strategy based on your application and the performance or redundancyyour application requires. Different levels of RAID offer different levels ofI/O performance.[ 93 ]