Date: Wed, 21 Mar 2001 22:17:21 +0100 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Mike Smith <msmith@freebsd.org> Cc: arch@freebsd.org Subject: Re: remind me again, why is MAXPHYS only 128k ? Message-ID: <89046.985209441@critter> In-Reply-To: Your message of "Wed, 21 Mar 2001 13:11:28 PST." <200103212111.f2LLBSh01790@mass.dis.org>
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In message <200103212111.f2LLBSh01790@mass.dis.org>, Mike Smith writes: >> >> Are there any roadblocks for increasing MAXPHYS as a tweakable these >> days, or is it still an "do not alter or ELSE..." #define ? > >There isn't much hardware out there that can do anything useful with an >I/O larger than 128k. Well, while that is true, things like striping and raid-5 could benefit from not being limited to a 128k stripesize for certain kinds of bulk application. I also belive tapes have been mentioned as a candidate for a larger MAXPHYS. >There was also a lengthy discussion on I/O >saturation a little while back; the short answer is just that making it >larger doesn't win anything significant, and may cause unacceptable >latencies in some cases. Right, I'm not asking for a general increase, I'm asking if it can be increased on a case-by-case basis or if the system will explode for arcane architectural reasons if I double or quadruple it on a particular system ? -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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