On 16/08/2011 18:42, Asdo wrote:
Hello all sometimes I put grub on the first sector of a MD raid1 device, which is on disk partition and not on the whole disk. (there is another bootloader in the MBR which chainloads this one, and that's not the problem) Sometimes, and I'm not yet able to reproduce it reliably, that sector gets zeroed at first reboot. So the first reboot after installation of the OS + grub indeed succeeds, but the next reboot fails. After the first reboot the first sector of such MD device gets zeroed, so at the second reboot the bootloader is missing. At that point I have to boot with a live-cd again and reinstall Grub in there to be able to boot again. I totally confirm that the sector is nonzero before the first reboot, and is zero after the second reboot. Not sure when exactly it gets zeroed but it's between those two points in time. I suspect it becomes zero at the first reassemble of the MD device. After the second reboot the problem won't ever happen again on that RAID. And if it hasn't happened by that time it won't ever happen again on that RAID. I'm thinking at a bug in some RAID initialization procedure which is being delayed at the first reassemble of the device... does this ring any bell? The last time it happened to me (that's yesterday) it was with a degraded raid-1 (it was created with a missing device) with metadata=1.0 . I absolutely confirm that dd'ing the first 512bytes sector from the MD device and dd'ing the first sector from the underlying partition both resulted in a (identical) nonzero sector before the first reboot. After the second reboot both were zero. Also please note that since it was a degraded raid-1, this excludes a resync problem, because there couldn't possibly have been any resync. Also, the filesystem itself appears intact, so this is a "bug" affecting only the very beginning of a MD device. Anyone knows what's happening?
The first sector of a md RAID with metadata 1.0 is in its data area, so there's no way md is writing to this area itself, it's almost certainly the filesystem that's writing it.
I think installing grub on a md partition is a bad idea. You can use metadata 1.2 to have the first 4K left free, but grub may write its stage 1.5 code to the first 31.5K of a device (whole drive or partition).
Cheers, John. -- 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
