Synchronous and Asynchronous I/O

[bang_dba]

hi,
What is the difference between Synchronous and Asynchronous I/O....
I read soome books...but couldn't understand propely. Can somebody explain the same with some simple example.

thanx

[slimdave]

if a process requests that the O/S write data to disk, and has to wait for it to be written before continuing, then that is synchronous. If the process does not have to wait for the write to be completed, that is asynchronous

[agasimani]

Synchronous is real-time, that is you ask to perform steps A,B,C, step B is done only after step A is completed, and C is done only when B is completed.

In Asynchronous, neither step B waits for A to complete, nor step C waits for B to complete.

[bang_dba]

hi
thanx for ur reply...

In case of asynchronous I/O if there is an error in writing to a block, then how this is taken care of

and again asynchronous i/o will be very fast i believe....is there any disadvantage with asynchronous I/O.

regards

[chao_ping]

With AIO enabled , sometimes you hit bugs, like AIO on aix jfs, and AIO on tru64 advfs.

[julian]

Originally posted by chao_ping
With AIO enabled , sometimes you hit bugs, like AIO on aix jfs, and AIO on tru64 advfs.

To add something about Solaris and HP UX. On Solaris, AIO is the default, on HP UX not: if you want to implement it, you will have to rebuild the kernel.

[agasimani]

In case of asynchronous I/O if there is an error in writing to a block, then how this is taken care of

This is the reason there are events called wait events.