Date: Thu, 22 Nov 2018 07:40:55 +0100 From: Matthias Petermann <matthias@petermann-it.de> To: freebsd-questions <freebsd-questions@freebsd.org> Cc: freebsd@johnea.net Subject: Re: newfs overwriting gmirror label? Message-ID: <911910aa-faa4-a081-6483-a45644512839@petermann-it.de> In-Reply-To: <5a8aadf8-8aa8-8cbb-61ab-0d9cc4b7e2c1@petermann-it.de> References: <5a8aadf8-8aa8-8cbb-61ab-0d9cc4b7e2c1@petermann-it.de>
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Hello, please ignore this posting. It looks like I did a mistake interpreting the hexdump. I did repeat the exercise and the result was that the gmirror label was not overwritten. Sorry for the confusion! Kind regards, Matthias Am 22.11.2018 um 06:56 schrieb Matthias Petermann: > Hello, > > this is somewhat related to my other post regarding GPT vs. GMIRROR. > Anyway, the following observation can be looked at in an isolated manner. > > I have documented the observation in a step-by-step protocol below. > > If you have some thoughts on this - please reply and let me know. I'd be > very thankful to get this clarified. > > Kind regards, > Matthias > > > > 0) Preface > > There is a gmirror set up, consisting of two components. I am going to > create a hex dump of the last block of one of the components, then fill > up the gmirror with a raw write of "FF" and create another hex dump of > one of the components. Then I will compare the hex dumps. > > 1) Checking gmirror label before manipulation > > 1FFFFDB0 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFDCC 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFDE8 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 47 45 4F 4D ........................GEOM > 1FFFFE04 3A 3A 4D 49 │ 52 52 4F 52 │ 00 00 00 00 │ 04 00 00 00 │ 74 65 > 73 74 │ 00 01 00 00 │ 00 00 00 00 ::MIRROR........test........ > 1FFFFE20 A0 07 5F E9 │ B0 49 4B F7 │ 73 07 3C A2 │ 02 00 00 00 │ 00 01 > 00 00 │ 00 00 00 10 │ 00 00 02 00 ._IKs.<................ > 1FFFFE3C FE FF 1F 00 │ 00 00 00 00 │ 02 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 40 .........................@ > 1FFFFE58 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 20 00 .......................... . > 1FFFFE74 00 00 00 BE │ 2B CF 02 21 │ 60 DB DE FB │ AB FC D2 03 │ 26 F6 > 64 00 │ 00 00 00 00 │ 00 00 00 00 ...+.!`.&d......... > 1FFFFE90 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFEAC 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFEC8 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFEE4 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFF00 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFF1C 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFF38 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFF54 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFF70 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFF8C 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFFA8 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFFC4 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFFE0 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ...................t.....@ . > > 2) Filling up mirror with "FF" > > root@l-mpe-fbsd:/home/admin # tr '\0' '\377' < /dev/zero > /dev/mirror/test > > 3) Checking gmirror label after manipulation > > 1FFFFDB0 FF FF FF FF │ FF FF FF FF │ FF FF FF FF │ FF FF FF FF │ FF FF > FF FF │ FF FF FF FF │ FF FF FF FF ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ > 1FFFFDCC FF FF FF FF │ FF FF FF FF │ FF FF FF FF │ FF FF FF FF │ FF FF > FF FF │ FF FF FF FF │ FF FF FF FF ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ > 1FFFFDE8 FF FF FF FF │ FF FF FF FF │ FF FF FF FF │ FF FF FF FF │ FF FF > FF FF │ FF FF FF FF │ 47 45 4F 4D ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒GEOM > 1FFFFE04 3A 3A 4D 49 │ 52 52 4F 52 │ 00 F8 FF FF │ 04 00 00 00 │ 74 65 > 73 74 │ 00 AF B4 80 │ FF FF FF FF ::MIRROR.▒▒▒....test.▒▒.▒▒▒▒ > 1FFFFE20 00 A8 CF 81 │ B0 49 4B F7 │ 73 07 3C A2 │ 02 00 00 00 │ 00 01 > 00 00 │ 00 00 00 10 │ 00 00 02 00 .▒▒.▒IK▒s.<▒................ > 1FFFFE3C FE FF 1F 00 │ 00 00 00 00 │ 02 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 40 ▒▒.........................@ > 1FFFFE58 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 20 00 .......................... . > 1FFFFE74 00 00 00 28 │ 37 37 D5 E2 │ 53 ED 72 2A │ 17 FC 86 3D │ FA 16 > 49 00 │ 00 00 00 00 │ 00 00 00 00 ...(77▒▒S▒r*.▒.=▒.I......... > 1FFFFE90 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFEAC 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFEC8 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFEE4 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFF00 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFF1C 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFF38 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFF54 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFF70 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFF8C 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFFA8 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFFC4 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFFE0 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 > 00 00 │ 00 00 00 00 │ 00 00 00 00 ............................ > 1FFFFFFC 00 00 00 00 │ .... > > 4) Conclusion > > So this looks like the gmirror label is not protected against low level > writes. Some bytes have been overwritten with "FF". > > So what I still would like to understand - how is it ensured that a > newfs will not touch this area? > > From my understanding, using the -r parameter of newfs could help, but > in none of the examples with gmirror using GPT partitions this is used. > So will the approach ultimately lead into gmirror label corruption (e.g. > once UFS is filled up)? > > -- Matthias Petermann <matthias@petermann-it.de> | www.petermann-it.de GnuPG: 0x5C3E6D75 | 5930 86EF 7965 2BBA 6572 C3D7 7B1D A3C3 5C3E 6D75
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