Date: Tue, 22 Oct 1996 11:15:18 +0200 (MET DST) From: Greg Lehey <grog@lemis.de> To: dgy@rtd.com (Don Yuniskis) Cc: questions@FreeBSD.org (FreeBSD Questions) Subject: Re: Making a DOS Partition writeable Message-ID: <199610220915.LAA00686@freebie.lemis.de> In-Reply-To: <199610220806.BAA21835@seagull.rtd.com> from Don Yuniskis at "Oct 22, 96 01:06:20 am"
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Don Yuniskis writes: > It seems that Doug White said: >> >> On Mon, 21 Oct 1996, Snob Art Genre wrote: >> >>>> Please, anyone correct me, but mounting a DOS-FS could -- under certain >>>> circumstances -- corrupt the BSD-FS !?!? >>> >>> Shortly after I installed FreeBSD, I was running two finds on different >>> virtual consoles, with /msdos mounted, and my machine crashed hard. When >>> it came back up, my entire FreeBSD installation was hosed. I can't say it >>> was definitely due to msdosfs, but I suspect it. >> >> The primary problem comes when you FIPS a partition and cause the cluster >> size to change. FreeBSD assumes a perfect world while FIPS cheats -- it >> SHOULD rewrite all those sectors back down to the smaller clustersize but >> that takes a while (I had a program that actually did it right!) esp. on >> big disks. > > So, how does this result in the FBSD partition being trashed? Or, is that > an "ugly rumor"? Is it only applicable to a FBSD partition on the same > physical device as a FIPS'ed DOS partition? etc. > > It sure would be nice if these things were more thoroughly described or > qualified ... help reduce some of the "lore" surrounding them. Good question. I've been holding back, since I don't use MS-DOS or its file systems, but my understanding was that FIPS leaves some pointers in the file system pointing outside the partition. I'd guess that the FAT is a good candidate here, since you can't shrink it easily. This doesn't seem to worry the native MS-DOS file systems (or I just haven't heard of it happening), but apparently it can cause FreeBSD's msdosfs to write outside in the area which belonged to the file system before it was truncated with FIPS. In the kind of situation we're looking at, where FIPS was used to make space for a FreeBSD file system, this will now be a FreeBSD file system. That's plausible, but I haven't personally seen any evidence that it has happened. If somebody else has, please speak up. Greg
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