Hi Jens, Thank you for your explanation. I have another question in regards to buffer_compress_percentage if you don't mind. If I were to call fio with "--refill_buffers --buffer_compress_percentage=0", would this be the same as setting only "--refill_buffers"? Also, if I were to call fio with "--refill_buffers --buffer_compress_percentage=100", would this be the same as setting "--zero_buffers"? Thanks again for your help! On Mon, May 27, 2013 at 1:21 AM, Jens Axboe <axboe@xxxxxxxxx> wrote: > On Fri, May 24 2013, Matthew Eaton wrote: >> Hello fio group, >> >> Can anyone tell me if --buffer_compress_percentage fills the buffer >> with random data and reuses that data or if it refills with random >> data for each submit? If you want the latter behavior should you >> combine with --refill_buffers? > > That is actually explained in the man page / HOWTO: > > buffer_compress_percentage=int If this is set, then fio will attempt to > provide IO buffer content (on WRITEs) that compress to > the specified level. Fio does this by providing a mix of > random data and zeroes. Note that this is per block size > unit, for file/disk wide compression level that matches > this setting, you'll also want to set refill_buffers. > > So the answer to your question is yes. Fio will reuse IO buffers, unless > --refill_buffers is set. If you do not set refill_buffers with > buffer_compress_percentage, then you will have identically compressible > blocks written. And that would only give you the per-block compression > ratio specified, on a broader scale it would compress more. > > -- > Jens Axboe > -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
