From owner-freebsd-current@FreeBSD.ORG Sun Mar 3 13:35:58 2013 Return-Path: Delivered-To: freebsd-current@FreeBSD.org Received: from mx1.freebsd.org (mx1.FreeBSD.org [8.8.178.115]) by hub.freebsd.org (Postfix) with ESMTP id 1BE091D9; Sun, 3 Mar 2013 13:35:58 +0000 (UTC) (envelope-from phk@phk.freebsd.dk) Received: from phk.freebsd.dk (phk.freebsd.dk [130.225.244.222]) by mx1.freebsd.org (Postfix) with ESMTP id D92DF7AA; Sun, 3 Mar 2013 13:35:57 +0000 (UTC) Received: from critter.freebsd.dk (critter.freebsd.dk [192.168.61.3]) by phk.freebsd.dk (Postfix) with ESMTP id B40178A57C; Sun, 3 Mar 2013 13:35:50 +0000 (UTC) Received: from critter.freebsd.dk (localhost [127.0.0.1]) by critter.freebsd.dk (8.14.5/8.14.5) with ESMTP id r23DZnYd052868; Sun, 3 Mar 2013 13:35:49 GMT (envelope-from phk@phk.freebsd.dk) To: Ian Lepore Subject: Re: access to hard drives is "blocked" by writes to a flash drive In-reply-to: <1362317291.1195.216.camel@revolution.hippie.lan> From: "Poul-Henning Kamp" References: <51323712.5000406@gmail.com> <20130303042043.GH286@server.rulingia.com> <1362317291.1195.216.camel@revolution.hippie.lan> Date: Sun, 03 Mar 2013 13:35:49 +0000 Message-ID: <52867.1362317749@critter.freebsd.dk> Cc: deeptech71 , freebsd-current@FreeBSD.org, Peter Jeremy X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 03 Mar 2013 13:35:58 -0000 Content-Type: text/plain; charset=ISO-8859-1 -------- In message <1362317291.1195.216.camel@revolution.hippie.lan>, Ian Lepore writes : >I run into this behavior all the time too, mostly on arm systems that >have an sd card or usb thumb driver as their main/only drive. This is really a FAQ and I belive I have answered it N times already: There are, broadly speaking, two classes of flash-storage: "Camera-grade" and "the real thing". "Camera-grade" have a very limited "Flash adaptation layer" which typically only can hold one flash-block open for writing at a time, and is typically found in CF and SD cards, USB sticks etc. Some of them gets further upset if the filesystem is not the FAT they expect, because they implement "M-Systems" (patented) trick with monitoring block deletes in FAT to simulate a TRIM facility. A number of products exist with such designs, typically a CF-style, is put behind a SATA-PATA bridge and sold as 2.5" SSD SATA devices. "Transcend" have done this for instance. If you use this class of devices for anything real, gstat will show you I/O write-times of several seconds in periodic pile-ups, even 100 seconds if you are doing something heavy. For various reasons (see: Lemming-syncer) FreeBSD will block all I/O traffic to other disks too, when these pileups gets too bad. -- 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.