Date: Mon, 5 Nov 2012 19:26:13 -0700 (MST) From: Warren Block <wblock@wonkity.com> To: Alexander Yerenkow <yerenkow@gmail.com> Cc: doc@freebsd.org Subject: Re: what's the deal with changing release notes? Message-ID: <alpine.BSF.2.00.1211051921090.87438@wonkity.com> In-Reply-To: <CAPJF9wncVOwVd-KErhzW4C1YLbfDWZ_GYNP-shPnJ_N9JMRFdA@mail.gmail.com> References: <CAF6rxgkEOcHCcJYiW0R9cZ4Nt8xeZP0bHVFC87Toqd_qr=Bgqw@mail.gmail.com> <CAF6rxgk2Fx6YhEkb9sfLbMYssZRSUuOo6ZURoeQVC6X96WuYnQ@mail.gmail.com> <CAPJF9w==3-DxibK3tLE2%2BP8SCMcrHJ-4Javja1OKOWK5pMeN7w@mail.gmail.com> <CAPJF9wncVOwVd-KErhzW4C1YLbfDWZ_GYNP-shPnJ_N9JMRFdA@mail.gmail.com>
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On Sun, 4 Nov 2012, Alexander Yerenkow wrote: > Can I add my 2c at this point? Where did 10240 appeared from? Did someone > tried to find some optimal size for most of flashes/cards? I always try to > use some large number, like 1m or even more. I know by sad experience that > writing flash with default bs can take much longer than with large bs value. > Very quick and dirty test (from dev/urandom to 1gb partition on sd card) > give me that speed numbers (bs, speed): > 128m = 11,38 > 8m = 11,42 > 512k = 11,46 > 10k = 1,10 > > So, default advice on how write those images are unoptimised. Drop in speed > by factor of ten without any reason not god as for me. Agreed. The 10K number also looks like a magic number, and it is not. Huge buffer sizes don't really improve speed, as your benchmark shows. There's no significant difference between 512K and 128M. I would suggest using 64K or 128K for the value. These are large enough to give speed benefits yet still small enough to work even if memory is very limited. Note: FreeBSD's dd is not case-sensitive about unit modifiers, but Linux is, so the example should stick to upper case "K".
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