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

[Tristan]

Sunil Mushran wrote:
> 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).

I knew what you meant, but I think my test probably don't need to do 
this, the verification step of comparing log_readed pattern with 
file_readed pattern  is suffice to  expose the fractured the  chunks. 
here the pattern I meant is chunk generated from log or read from file 
is one chunk in memory.

The log_readed pattern is generated from a log record, which has 
definitely the same header and trailer, so if the corresponding pattern 
in file didn't have a same header and trailer, it can be easily revealed 
by a simple comparison.


Tristan.
>
> 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).