Date: Tue, 13 Nov 2012 14:07:50 -0800 From: "Ronald F. Guilmette" <rfg@tristatelogic.com> To: freebsd-questions@freebsd.org Subject: Re: Advanced Format Drive ? Message-ID: <4073.1352844470@tristatelogic.com> In-Reply-To: <20121113073030.87bc0608.freebsd@edvax.de>
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In message <20121113073030.87bc0608.freebsd@edvax.de>, Polytropon <freebsd@edvax.de> wrote: >Note that 4k = 8 x 512 byte, and so 64 sectors would be a >good alignment "grid", while 63 sectors is not. That implies >that in case you use fdisk to create a slice holding your >partitions, try to make it start at sector 64 (63 would >have been the default). OK. I've only ever used the FreeBSD fdisk to just look at what the current (DOS) partitioning is, so I guess I'll have to dig into the man page and try to figure out how to actually use it to create a DOS partition starting at "block" 64. >After that, use bsdlabel to create the partitions inside >the slice as you want. Make them multiples of 1M or 1G, OK. I think that I always was doing that anyway. But I want to be sure that I understand... If the size of the BSD partition is a multiple of, say, !MB, then the _alignment_ of that partition will likewise (auto- magically) be at least 1MB also? Or do I need to set the alignment separately, e.g. my manually running bsdlabel? (Normally, I've just been using what noadays is being called "guided" partitioning, you know, with the friendly curses-based GUI. So As with fdisk, I have no real experience using bsdlabee from teh command line. But I guess it is time that i learned how.) >that should be no big deal because disks are big and cheap >today. :-) Yes, exactly so. I am not exactly going to sweat losing even, say, one megabyte now that I am the proud owner of a shiny new one TERABYTE drive. (Thirty years ago, I could hardly have even ever imagined that such might exist one day, let alone that I myself would own one, and let alone that I might have been able to purchase one for less than $100 USD. Rather amazing really.) >You can then easily use newfs with the -f parameter: > > newfs -U -f 4096 <device> > >This will make sure the proper fragment size will be applied >upon formatting the created partitions. OK. Thanks. I am guessing that this is really the one and probably _only_ thing that might really make any significant difference, performance- wise, right? I mean if the partition is improperly aligned, that really only would affect reading and/or writing at the very beginning or at the very end of the partition, right? Whereas this -f parameter for newfs is, I gather, the thing that really tells the kernel the size of the physical chunks of data that it can/should read/write to the drive at any one time, right? And while we are on the subject... Has anybody ever down any analysis (i.e. benchmarking) to find out if -f 4096 is even the best number for a modern high(er) capacity drive? I'm just sort-of wondering if 8192 or 16384 might be better.
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