On 20/03/17 17:37, Peter Sangas wrote: >> From: Wols Lists [mailto:antlists@xxxxxxxxxxxxxxx] >> NEVER NEVER NEVER use --create !!! >> >> >> Use something like --assemble --force, which will set up a working array > if it can. > > OK, I tried this command but received an error: > > mdadm --assemble --force /dev/md10 /dev/sdc > > "Cannot assemble mbr metadata in /dev/sdc, no superblock" > > What command do you suggest...? > That makes it sound like something had trashed the superblock, or maybe it was sdc1, or something. Anyways, it worked for you, so hopefully the question is academic. > > >> If that had been an old array, with a different offset or superblock or > the like... > > by "old" do you mean an array created using a different superblock format > other than 1.2? > Yes. The superblock format is v1. Whether it's v1.0, v1.1 or v1.2 depends on where the superblock is found. So if, for example, the array had been created with a v1.0 superblock, the data would probably have started at offset 2048, with the superblock at the end of the disk. v1.2 puts the superblock near the start, maybe offset 4096? So you would have smashed some of your data, and also told the array to look in the wrong place for the start of the data. That's why --create is so dangerous - pick the wrong version and you can damage the data, but even if you pick the right version, all the default offsets and things have changed over the years (that's assuming they haven't also been modified by general array management), so you can easily lose where the data area starts. Cheers, Wol -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
