Re: Possible bug when setting compression

[Jens Axboe <axboe@kernel.dk>]

On 03/14/2014 03:06 PM, Matthew Eaton wrote:
>> zero_buffers and buffer_compres_percentage=100 are essentially the same
>> thing, for both cases it writes buffers just fill of zeroes. So I'm not sure
>> what you were expecting here since you don't think it works as it should?
>>
>> If you have both zero_buffers and scramble set, then the result will be a
>> bit less compressible. The goal of scramble_buffers is to defeat basic
>> dedupe attempts. So even if you don't fully refill your buffers every time,
>> the blocks will be a bit different.
>>
>> --
>> Jens Axboe
>>
>>
>
> Hmm, I was assuming that scramble_buffers shouldn't have any effect
> since it's scrambling all zeros.  Is scramble_buffers inserting random
> data even with zero_buffers set?

scramble_buffers tells fio to randomly insert some data in the buffer. 
It's not a full overwrite or anything like that, just some basic garbage 
for each 512b to prevent naive compression/dedupe.

-- 
Jens Axboe