#DSYNC REVIEW MAC WINDOWS#

On the other hand, it is common to turn off dsync on devices of databases which do not need to be recovered like the tempdb. Please also note that a cache and a buffer are different.ĭsync is always on for the master device: the performance of writes there is not critical and it’s important that it can be fully recovered. It just means that when you write synchronously or check for whether the asynchronous I/O was performed, you’ll only get the response that the write is completed once the data are effectively on the physical disk.

It should be noted that dsync doesn’t mean that there is not asynchronous I/O. The drawback of dsync is that it costs performance (because the writes, even if buffered by the OS, are guaranteed to go to the disk before the operation finishes). The data could still be in the disk write cache and get lost… Of course, this only handles OS level buffering. This allows for a better recoverability of the written data in case of crash: If the writes are buffered by the OS and the system crashes, these writes are lost.

#DSYNC REVIEW MAC WINDOWS#

First, dsync has no effect on raw devices (i.e., a device on a raw partition) and on devices on Windows operating system (i.e., it only affects Unix/Linux operating systems).ĪSE opens a database device file of a device with the dsync setting on, using the operating system dsync flag.With this flag, when ASE writes to the device file, both the written data must be physically stored on disk before the system call returns.

Dsync review mac