about the write order fidelity. I know that filesystems guarantee that. Looking from filesystem perspective, no write will be allowed on the same block until
the first write finishes. So, if 'B' is written after 'A' you can always guarantee that you will see 'B' at the end of the two writes.
Now imagine not having a filesystem, and doing a write directly on the device. Do device drivers honour it. Should they? I imagine device driver as a kind of
queue. So any writes are always queued up one after the other so that it gives write order fidelity whether it wants to or not. Am i missing something here.
Regards,
Neha
On Fri, Aug 2, 2013 at 1:56 PM, Greg Freemyer <greg.freemyer@xxxxxxxxx> wrote:
On Fri, Aug 2, 2013 at 1:32 AM, Rajat Sharma <fs.rajat@xxxxxxxxx> wrote:But it can't ..... unless the write cache is turned off and it is
> On Fri, Aug 2, 2013 at 2:25 AM, neha naik <nehanaik27@xxxxxxxxx> 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.
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
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