Date: Tue, 23 Apr 2019 16:04:18 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: avg@FreeBSD.org Cc: bugs@freebsd.org Subject: Re: [Bug 202712] [cam] [ata] System doesn't recognize older hdd after boot Message-ID: <20190423154851.A9443@besplex.bde.org> In-Reply-To: <bug-202712-227-ujClAushAB@https.bugs.freebsd.org/bugzilla/> References: <bug-202712-227@https.bugs.freebsd.org/bugzilla/> <bug-202712-227-ujClAushAB@https.bugs.freebsd.org/bugzilla/>
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On Mon, 22 Apr 2019 a bug that doesn't want replies@freebsd.org wrote: > https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=202712 > > --- Comment #21 from Andriy Gapon <avg@FreeBSD.org> --- > (In reply to Domagoj Hranjec from comment #20) > And my point is that I am not sure if you have actually tested reading from the > end of the disk with the older FreeBSD. I am not sure that the older FreeBSD > reads sectors at the end for tasting and that any of the files you accessed > have blocks sufficiently close to the end. > But I do not insist that my hypothesis is correct. > Bruce has suggested another one, for instance. Old ATA also has, and sometimes uses, a feature of limiting the drive's size reported by the IDENTIFY command (IIRC, the struct contains the limited and unlimited sizes, but old drivers only look in the old parts of the struct which only have the limited size). Even without that, if the drive supports both CHS and LBA and the driver changes between them, there is a chance of getting different sizes depending only whether the last "cylinder" ink the fake geometry can be partial. Old CHS geometries are closer to physical. Not so old drives that support LBA usually have a non-physical geometry with 15 fake heads, and also round the total number of sectors so that the last cylinder in the fake geometry isn't partial. Usually the total number of sectors reported in the boot messages is the actual number of accessible sectors for the current configuration, so you can tell if there are unreadable blocks at the end are from this number changing. Bruce
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