Date: Sun, 4 Jun 2017 09:52:36 +0200 From: Hans Petter Selasky <hps@selasky.org> To: Tomoaki AOKI <junchoon@dec.sakura.ne.jp>, freebsd-current@freebsd.org Subject: Re: Time to increase MAXPHYS? Message-ID: <15e42fd1-055d-28f6-5e24-1448e16954a9@selasky.org> In-Reply-To: <20170604163948.eb5f74ce2a233b8f204ba671@dec.sakura.ne.jp> References: <0100015c6fc1167c-6e139920-60d9-4ce3-9f59-15520276aebb-000000@email.amazonses.com> <972dbd34-b5b3-c363-721e-c6e48806e2cd@elischer.org> <3719c729-9434-3121-cf52-393a4453d0b2@freebsd.org> <CANCZdfrkc1ERKnJr4JzHpePmU%2BrN5JOgAVePCShPHLDCAE19=w@mail.gmail.com> <CANCZdfpD3G8gR=C2_AekM6VeJ6dzKOnP820OOoF1M_eS0MfJ3g@mail.gmail.com> <20170604163948.eb5f74ce2a233b8f204ba671@dec.sakura.ne.jp>
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On 06/04/17 09:39, Tomoaki AOKI wrote: > Hi > > One possibility would be to make it MD build-time OTIONS, > defaulting 1M on regular systems and 128k on smaller systems. > > Of course I guess making it a tunable (or sysctl) would be best, > though. > Hi, A tunable sysctl would be fine, but beware that commonly used firmware out there produced in the millions might hang in a non-recoverable way if you exceed their "internal limits". Conditionally lowering this definition is fine, but increasing it needs to be carefully verified. For example many USB devices are only tested with OS'es like Windows and MacOS and if these have any kind of limitation on the SCSI transfer sizes, it is very likely many devices out there do not support any larger transfer sizes either. --HPS
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