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Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Lawrence D'Oliveiro <ldo@nz.invalid> Newsgroups: comp.os.vms Subject: Re: RX2800 sporadic disk I/O slowdowns Date: Sun, 20 Oct 2024 01:25:43 -0000 (UTC) Organization: A noiseless patient Spider Lines: 14 Message-ID: <vf1m6n$444r$2@dont-email.me> References: <veu99d$3derp$1@dont-email.me> <veumb8$3gbt8$1@dont-email.me> <vf1ku6$3vhv$1@dont-email.me> <vf1lvv$3s2a$1@dont-email.me> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Sun, 20 Oct 2024 03:25:43 +0200 (CEST) Injection-Info: dont-email.me; posting-host="bebb5afd8d6b363c1d85744b8b6ba226"; logging-data="135323"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+xOGEXMc8Kvf9ntvMd3yQm" User-Agent: Pan/0.160 (Toresk; ) Cancel-Lock: sha1:fI71ABn3DaS5MlhvZt96cCAHXcE= Bytes: 1540 On Sat, 19 Oct 2024 21:22:08 -0400, Arne Vajhøj wrote: > On 10/19/2024 9:04 PM, Lawrence D'Oliveiro wrote: > >> Here’s another question: why does a disk controller need a battery- backed- >> up cache? Or indeed any cache at all? > > Better performance. Think about it: the OS already has a filesystem cache in main RAM. That runs at main RAM speeds. Whereas the disk controller is connected through an interface to the CPU suitable only for disk I/O speeds. So any disk controller cache is on the wrong side of that interface.