From owner-freebsd-hackers@freebsd.org Sun Jan 22 00:08:13 2017 Return-Path: Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 0554ECB016C; Sun, 22 Jan 2017 00:08:13 +0000 (UTC) (envelope-from jmg@gold.funkthat.com) Received: from gold.funkthat.com (gate2.funkthat.com [208.87.223.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "gold.funkthat.com", Issuer "gold.funkthat.com" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id C825C6A; Sun, 22 Jan 2017 00:08:12 +0000 (UTC) (envelope-from jmg@gold.funkthat.com) Received: from gold.funkthat.com (localhost [127.0.0.1]) by gold.funkthat.com (8.15.2/8.15.2) with ESMTPS id v0LNpVDb043310 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Sat, 21 Jan 2017 15:51:31 -0800 (PST) (envelope-from jmg@gold.funkthat.com) Received: (from jmg@localhost) by gold.funkthat.com (8.15.2/8.15.2/Submit) id v0LNpVBV043309; Sat, 21 Jan 2017 15:51:31 -0800 (PST) (envelope-from jmg) Date: Sat, 21 Jan 2017 15:51:31 -0800 From: John-Mark Gurney To: Aijaz Baig Cc: "Greg 'groggy' Lehey" , FreeBSD Hackers , freebsd-scsi@freebsd.org Subject: Re: Understanding the rationale behind dropping of "block devices" Message-ID: <20170121235131.GF1768@funkthat.com> Mail-Followup-To: Aijaz Baig , Greg 'groggy' Lehey , FreeBSD Hackers , freebsd-scsi@freebsd.org References: <20170116071105.GB4560@eureka.lemis.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Operating-System: FreeBSD 11.0-ALPHA2 amd64 X-PGP-Fingerprint: D87A 235F FB71 1F3F 55B7 ED9B D5FF 5A51 C0AC 3D65 X-Files: The truth is out there X-URL: https://www.funkthat.com/ X-Resume: https://www.funkthat.com/~jmg/resume.html X-TipJar: bitcoin:13Qmb6AeTgQecazTWph4XasEsP7nGRbAPE X-to-the-FBI-CIA-and-NSA: HI! HOW YA DOIN? can i haz chizburger? User-Agent: Mutt/1.6.1 (2016-04-27) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.4.3 (gold.funkthat.com [127.0.0.1]); Sat, 21 Jan 2017 15:51:31 -0800 (PST) X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 22 Jan 2017 00:08:13 -0000 Aijaz Baig wrote this message on Mon, Jan 16, 2017 at 14:19 +0530: > Nevertheless my question still holds. What does 'removing support for block > device' mean in this context? Was what I mentioned earlier with regards to > my understanding correct? Viz. all disk devices now have a character (or > raw) interface and are no longer served via the "page cache" but rather the > "buffer cache". Does that mean all disk accesses are now direct by passing > the file system?? One of the other reasons block devices were removed was that if there was a write error on the underlying device, there was no way for the writer to know that the write failed. This could/would lead to corrupted data which is bad. -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."