Conceptual questions about device driver

[Greg Freemyer]

On Fri, Aug 2, 2013 at 1:32 AM, Rajat Sharma <fs.rajat at gmail.com> wrote:
> On Fri, Aug 2, 2013 at 2:25 AM, neha naik <nehanaik27 at gmail.com> wrote:
>> Hi,
>>  I have some conceptual questions about device driver :
>>
>> 1. Write order fidelity should be maintained when submitting requests from
>> device driver to disk below.
>>     However, acknowledging these requests it is okay if we don't necessarily
>> maintain that order, right?
>>
>
> Yes it should not matter as long as application can rely on data being
> written is in order of submission.

But it can't ..... unless the write cache is turned off and it is
known the the cache is truly off.

There is no guarantee of write order in the block stack.  Not between
the filesystem and the driver.  Not between the driver and the drive.

There are at least 2 elevators shuffling the order of writes to
optimize performance.

Rajat, did you get confused?  Or were you trying to say something else?

Greg