[Ocfs2-test-devel] [PATCH 1/1] Ocfs2-test: Add destructive testcase for reflink_test v1.

[Sunil Mushran]

Tristan wrote:
> Not quite sure if I get what you mean exactly,  I think comparing the 
> timestamp in header with the latest one in logfile is enough to ensure 
> if the last write hit the disk. why to compare the header with trailor, 
> it should be the same since we only reboot the machine after a 
> successful write, and each will guarantee the header do is the same as 
> trailor.

The reason we want to compare the header with the trailer is to look
for fractured chunks. Remember the io that the user submits goes thru
many layers in the kernel and then to the storage. If the IO to the chunk
gets broken down into per block, then a well timed machine reset could
result in an inconsistent chunk (fractured).

This is one reason why we ask users to use a clustersize of atleast the
oracle db blocksize as that ensures that each oracle block is contiguous
on disk, which allows the io stack in linux to keep the ios to it whole
(and not break it up into smaller blocks).