From owner-freebsd-hackers@FreeBSD.ORG Fri Nov 1 19:36:01 2013 Return-Path: Delivered-To: hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTP id 20212840; Fri, 1 Nov 2013 19:36:01 +0000 (UTC) (envelope-from jmg@h2.funkthat.com) Received: from h2.funkthat.com (gate2.funkthat.com [208.87.223.18]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id D6919237D; Fri, 1 Nov 2013 19:36:00 +0000 (UTC) Received: from h2.funkthat.com (localhost [127.0.0.1]) by h2.funkthat.com (8.14.3/8.14.3) with ESMTP id rA1JZr3A075368 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Fri, 1 Nov 2013 12:35:54 -0700 (PDT) (envelope-from jmg@h2.funkthat.com) Received: (from jmg@localhost) by h2.funkthat.com (8.14.3/8.14.3/Submit) id rA1JZrcE075367; Fri, 1 Nov 2013 12:35:53 -0700 (PDT) (envelope-from jmg) Date: Fri, 1 Nov 2013 12:35:53 -0700 From: John-Mark Gurney To: Warren Block Subject: Re: GEOM mentor request Message-ID: <20131101193553.GE73243@funkthat.com> Mail-Followup-To: Warren Block , symbolics@gmx.com, geom@freebsd.org, hackers@freebsd.org References: <20131101103158.GA35397@lemon> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.3i X-Operating-System: FreeBSD 7.2-RELEASE i386 X-PGP-Fingerprint: 54BA 873B 6515 3F10 9E88 9322 9CB1 8F74 6D3F A396 X-Files: The truth is out there X-URL: http://resnet.uoregon.edu/~gurney_j/ X-Resume: http://resnet.uoregon.edu/~gurney_j/resume.html X-to-the-FBI-CIA-and-NSA: HI! HOW YA DOIN? can i haz chizburger? X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.2 (h2.funkthat.com [127.0.0.1]); Fri, 01 Nov 2013 12:35:54 -0700 (PDT) Cc: geom@freebsd.org, hackers@freebsd.org, symbolics@gmx.com X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 01 Nov 2013 19:36:01 -0000 Warren Block wrote this message on Fri, Nov 01, 2013 at 13:23 -0600: > On Fri, 1 Nov 2013, symbolics@gmx.com wrote: > > > + Implement new things. Some ideas I have had: > > + GEOM "ERASE" - Rewrite deletes into random writes. > > + GEOM "PLUG" - Persistent version of the connect/disconnect verbs > > where the flag sits in the class metadata. This might be a cleaner > > approach, rather than adding the verbs to all the existing > > providers. > > + GEOM "TAP" - Allow userspace processes to hook into the GEOM > > API. Intended for debugging and development. > > + GEOM "WCACHE" - Allow you to use small, fast provider as a buffer > > for a larger, slower provider. > > + GEOM DTrace provider. Provide GEOM specific probes to complement > > the IO provider. > > + Probably other bits I can't remember right now. > > How about an explicit geom retaste command? "true > /dev/ada0" is > misleading to the reader. > > Also, a RAM-cached version of gmirror that would report writes finished > as soon as the faster drive finishes. Kind of the opposite of the > WCACHE above. This would permit creating mirrors of an SSD and hard > drive without performance loss, at least up until available write > buffer space runs out. This one may not be so easy. If you did that, you'd want to do something like set the SSD to prefer, and only complete on that drive.. That way if there is ever a crash, you mirror the second disk from the faster first... Though this still has the possibility to leave your fs is a inconsistent state as once the write for the faster drive completes, another write could come in and complete on the second drive before the first IO completes breaking the assumptions that UFS+S and ZFS about how/when IO gets committed to the disk... Also, depending upon the write load, it could be the HD is faster than the SSD if there was a large enough volume of writes... -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."