From owner-freebsd-questions@FreeBSD.ORG Mon Jul 16 15:50:32 2012 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id AC6151065670 for ; Mon, 16 Jul 2012 15:50:32 +0000 (UTC) (envelope-from jerry@seibercom.net) Received: from mail-yw0-f54.google.com (mail-yw0-f54.google.com [209.85.213.54]) by mx1.freebsd.org (Postfix) with ESMTP id 4827B8FC1C for ; Mon, 16 Jul 2012 15:50:32 +0000 (UTC) Received: by yhfs35 with SMTP id s35so6168228yhf.13 for ; Mon, 16 Jul 2012 08:50:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=seibercom.net; s=google; h=date:from:to:subject:message-id:in-reply-to:references:reply-to :organization:x-mailer:face:mime-version:content-type :content-transfer-encoding; bh=F+lBmOsi2YOodMvSdv8R0TY44gHzpHe5WK8ElHwZ68U=; b=j6DV6ymxbiFTL603FFTA4uPfosFKcWugsDIH5xn6tXk5Z/zA1+NBfFlfBnz53JkE0n e8Ti4vzFIjm2kUzIyLY5mxCqgPkFcVdwB3/SDuI4m+aytph/o8EVhhDi7fv/xBUvZRu6 SiProjY8Ulc8uldZV6Jqb1LGQYnMUs/kthwos= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=date:from:to:subject:message-id:in-reply-to:references:reply-to :organization:x-mailer:face:mime-version:content-type :content-transfer-encoding:x-gm-message-state; bh=F+lBmOsi2YOodMvSdv8R0TY44gHzpHe5WK8ElHwZ68U=; b=YqoerMMxilm07VyXmLbelUG27wYrxzOgvqnX+4hirUwrWxR7pJ6Q8nFM3a+pm0LYeA 8sPBOZ6C9j/MLbizKpu7zN0zJbhkP15x46E4o0Tray4isQVT/fZoYqm25uvxOuZq3pnc 0vIZs9uxVn4hlkr1sRXTpoDXXTMouBsqriYd+99C1aGIdvuUhZJpG+K2AwPzMoPDh3AI cvH+cbKTCPFgsdBHEGMNqMXgUyl5y1R7qDTKErdVphzYZY+U5oeMO2BgTUiQ3/UPWWf6 5S/8zZpDCymkszEtQ8iAmxKNnRzYNk0O1SpLyYxkjscOq8t2nRbafwepPLpn+wW2bnmO XOZQ== Received: by 10.236.76.5 with SMTP id a5mr9924181yhe.8.1342453826031; Mon, 16 Jul 2012 08:50:26 -0700 (PDT) Received: from scorpio.seibercom.net (cpe-076-182-104-150.nc.res.rr.com. [76.182.104.150]) by mx.google.com with ESMTPS id a7sm25779647yhm.0.2012.07.16.08.50.24 (version=TLSv1/SSLv3 cipher=OTHER); Mon, 16 Jul 2012 08:50:25 -0700 (PDT) Received: from scorpio (localhost [127.0.0.1]) (using TLSv1.2 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) (Authenticated sender: jerry@scorpio.seibercom.net) by scorpio.seibercom.net (Postfix) with ESMTPSA id 3WbTbf5kRyz2CG62 for ; Mon, 16 Jul 2012 11:50:22 -0400 (EDT) Date: Mon, 16 Jul 2012 11:50:22 -0400 From: Jerry To: FreeBSD Message-ID: <20120716115022.68940af1@scorpio> In-Reply-To: <201207161404.q6GE4VrC001138@mail.r-bonomi.com> References: <201207161404.q6GE4VrC001138@mail.r-bonomi.com> Organization: seibercom.net X-Mailer: Claws Mail 3.8.1 (GTK+ 2.24.6; amd64-portbld-freebsd8.3) Face: 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 Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Gm-Message-State: ALoCoQnV+LcJnhxV2MReNEONTu+ikiIs9xsjGKkufV6fgV3L+5ewsGCgOIJv8LbU2Jgifl/9H/Mc Subject: Re: fsck on FAT32 filesystem? X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: FreeBSD List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 16 Jul 2012 15:50:32 -0000 On Mon, 16 Jul 2012 09:04:31 -0500 (CDT) Robert Bonomi articulated: > > From owner-freebsd-questions@freebsd.org Sun Jul 15 16:31:45 2012 > > Date: Sun, 15 Jul 2012 23:29:39 +0200 (CEST) > > From: Wojciech Puchar > > To: FreeBSD > > Subject: Re: fsck on FAT32 filesystem? > > > > > totally in error. SpinRite will attempt to read a damage sector > > > up to 2000 times and through different algorithms determine what > > > is most > > > > man dd > > > > conv=sync,noerror > > This is *precisely* why dd is _grossly_inferior_ to > professional-grade tools like Spinrite. > > With the settings the resident "infallible expert on everything" > <*SNORT*> recommends, dd will make _one_ attempt to read each disk > sector, going through the O/S's device driver code, and write out > 'whatever it got', regardless of whether or not ane sort of > read-error was signalled. This results in GUARANNTEED, > *UNRECOVERABLE*, GARBAGE in the copy, _every_ place where a read > error was encountered. This result can be marginally acceptable -- > for 'first-cut' attempts at accessing 'easily recoverable' data on > the disk. > > 'dd' is purely 'amateurville', however, when it comes to recovering > =critical= data inside an 'unreadable' (by the O/S) disk block. > > > Spinrite, and other professional-grade tools, run absolutely > stand-alone, without the use of _any_ O/S drivers, or even BIOS > code. Spinrite _directly_ programs the hard-disk-controller chip, > can retrieve into memory _every_ bit -- including address-marks, > sector framing, recorded ECC bits, and so on -- on a track, for > analysis, can seek from an inner track, read the bits, then seek from > an _outer_ track, and do another read. It can also do things like > step the heads 'fractionally' off the track center, and read > _there_. By doing these kinds of *very*low*level* operations, that > are forbidden to any 'userland' task, by an O/S, tools like Spinrite > can do a FAR BETTER job of extracting data from damaged disks. > > Professional-grade tools can also do things like 'pre-initialize' the > I/O buffer _in_the_disk_itself_, with _different_ bit patterns on > multiple read passes, They can thus find bitstrings that are (a) the > 'prior data' in th buffer, (b) bits that are read consistently from > the disk, and (c) bits that 'change value' from one read attempt to > the next. This allows such tools to do a much better job of > RECONSTRUCTING the actual data in the 'error' sector(s). > > > "Make a copy, and work only on the copy" _is_ good advice for > attempting 'simple' data recovery with tools that run in 'userland', > under an O/S. When the 'simple' approach fails, or is insufficient, > it is time to bring out the "big guns" -- things like Spinrite -- > which -require- direct accesss to the original damaged disk. Since > Spinrite, and similar tools, operate READ-ONLY on the disk -- which > is *not* guaranteed if there is a general-purpose O/S in the wa -- it > _is_ generally safe to let them access the damaged original. The > problematic situation is where spinning up the drive causes -more- > damage to the media.. +1 I use to keep SpinRite on a flash drive that I could easily carry with me if needed. Of course that would require the machine to be worked on to have the ability to boot from a flash drive. Unfortunately, not all of them could. Fortunately, I almost never need an industrial strength recovery product like SpinRite. It is nice to know it is available if I do though. -- Jerry ♔ Disclaimer: off-list followups get on-list replies or get ignored. 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