From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <532375B6.1060208@kernel.dk> Date: Fri, 14 Mar 2014 15:33:42 -0600 From: Jens Axboe MIME-Version: 1.0 Subject: Re: Possible bug when setting compression References: <532349BF.4010307@kernel.dk> <532361FE.10901@kernel.dk> <53236538.2040903@kernel.dk> <53236D0B.5040507@kernel.dk> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit To: Matthew Eaton Cc: fio@vger.kernel.org List-ID: 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