2010/1/6 Alexander Motin <m...@freebsd.org>: > Ivan Voras wrote: >> I think there was one more reason - though I'm not sure if it is still >> valid because of your current and future work - the MAXPHYS >> limitation. If MAXPHYS is 128k, with 64k stripes data was only to be >> read from maximum of 2 drives. With 4k stripes it would have been read >> from 128/4=32 drives, though I agree 4k is too low in any case >> nowadays. I usually choose 16k or 32k for my setups. > > While you are right about MAXPHYS influence, and I hope we can rise it > not so far, IMHO it is file system business to manage deep enough > read-ahead/write-back to make all drives busy, independently from > MAXPHYS value. With small MAXPHYS value FS should just generate more > requests in advance. Except some RAID3/5/6 cases, where short writes > ineffective, MAXPHYS value should only affect processing overhead.
Yes, my experience which lead to the post was mostly on UFS which, while AFAIK it does read-ahead, it still does it serially (I think this is implied by your experiments with NCQ and ZFS vs UFS) - so in any case only 2 drives are hit with 64k stripe size at any moment in time. In any case, as you say it is tunable so personal preferences can be applied. Thanks! _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
