Hi Wolf, thanks for your great input again!
(see below) On 04/30 09:27, Wynn Wolf Arbor wrote: > All the following assuming that the disk was originally partitioned as GPT, > but after that exclusively accessed as an MBR disk. > > > PT fdisk (gdisk) version 1.0.5 > > > > Caution: invalid main GPT header, but valid backup; regenerating main header > > from backup! > > This makes sense since the GPT backup at the very end of the disk would most > likely still be intact. gdisk identifies it correctly, but assumes (wrongly) > that the data on the disk is governed by the GPT layout. > > Since the disk was only ever accessed through an operating system that knew > solely about MBR, the GPT data meant nothing to it. It happily wrote data > past the MBR headers. Because the protective MBR is positioned before GPT > information, the primary GPT header was destroyed and most likely > overwritten with the file system. See also [1], the actual file system data > probably begins somewhere past LBA 0. > > > Caution! After loading partitions, the CRC doesn't check out! > > Warning: Invalid CRC on main header data; loaded backup partition table. > > Warning! Main and backup partition tables differ! Use the 'c' and 'e' > > options > > on the recovery & transformation menu to examine the two tables. > > This is because the backup GPT written when first partitioned does no longer > match the data present at the very beginning of the disk. > > If the initial assumption is correct, GPT *must not* be restored. Your > modern PC sees the GPT partition type and assumes the existence of a GPT. It > should, however, access the MBR layout and interpret the partition marked > with the GPT ID as a regular partition. > > Now, how to fix this? > > Like Andrea already said earlier: > > > Since the disk is only 1TB, there is no reason to use GPT at all, so > > your best bet is to use fdisk to make that a standard MBR by changing > > the partition type from 'ee' to '83'. > > This would *not* repartition or reformat any data, it would simply tell your > modern operating system to access the protective partition as a regular one. > > It would, however, require writing the new type to disk. What you could do > to be more safe here is to take a backup of the first 512 bytes with `dd', > then change the partition ID with `fdisk', and try mounting it. > > If it works, great. If not, you can restore the first 512 bytes of the disk > with the backup. > > > "fix manually" scares me...especially because I have no place for > > 1TB of an image file to with which I can experiment ... > > > Any ideas which could ease my burden and to un-scare my > > "need to fix it manually" ??? ;) ;) > > There's a few alternatives: > > 1) Boot an older system that only understands MBR, and mount the disk there. > This was suggested earlier but was dismissed because we assumed the sector > size had something to do with it. I do not think this is the case anymore - > the old system should be able to read it. > > 2) Boot a VM with a kernel that only understands MBR, pass USB through to > the virtual machine, mount the disk there. > > 3) Try confirming that there exists file system data past the MBR header. > > Maybe something like this: > > # dd if=/dev/sdb of=sdb-data bs=512 skip=1 count=16384 > $ file sdb-data > > As established, the block size is 512 bytes. We skip the first 512 bytes > since that is the protective MBR. sdb-data should then contain the first > 8MiB worth of actual file system data. The `file' utility can tell you what > kind of data it is. > > [1] > https://en.wikipedia.org/wiki/GUID_Partition_Table#/media/File:GUID_Partition_Table_Scheme.svg > > -- > Wolf > I had booted into my old system, attached the disks and both show the same behaviour: Only the device itself (/dev/sdb) was recognized. 'file' shows the following output: file sdb-data sdb-data: Linux rev 1.0 ext4 filesystem data, UUID=2f063705-0d3a-4790-9203-1b4edab7788c (extents) (64bit) (large files) (huge files) Looks better than I have thought...or? I will take a deeper look tommorrow...I am too tired to "fix partition tables manually" this evening! Read you tommorrow! :) Cheers! Meino
