Date: Mon, 14 Sep 1998 18:11:38 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: joelh@gnu.org Cc: tlambert@primenet.com, tom@uniserve.com, gpalmer@FreeBSD.ORG, irc@cooltime.simplenet.com, freebsd-current@FreeBSD.ORG Subject: Re: Download of FreeBSD 3.0-SNAP Message-ID: <199809141811.LAA18415@usr05.primenet.com> In-Reply-To: <199809141738.MAA08622@detlev.UUCP> from "Joel Ray Holveck" at Sep 14, 98 12:38:54 pm
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> I'm no disk expert, so please tell me: what is tagged command > queueing? Is it the ability to have multiple outstanding requests, > with the device reordering the requests for optimal efficiency, and > relying on a cookie in the header to differentiate between requests? Yes. Think of it as "how much concurrency does my disk support?". For a single-user, sincgle-program-at-a-time system, this is not much of a bottleneck; for a server under load, it's the *primary* bottleneck. Note that David points out that FreeBSD *does* do elevator sorting; it's still not optimal, however, since physical and logical cylinder boundaries are infrequently the same on modern hardware. I have to look before I say any more (since I thought the code was removed circa 2.2.1). David says it's called on all "dumb" drivers (wd, etc.); I'm not sure the "Ultra" DMA EIDE drivers are still in this category. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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