Hi Francesco, As far as I can determine reading this thread you have had a RAID1 with two disks sda and sdb. The disk sda failed. But grub was only installed on the failed sda. The disk sdb contains a mirror of everything but does not boot. Earlier in the thread Lennart gave an excellent suggestion: Lennart Sorensen wrote: > You can boot the install disk in rescue mode, select the root > partition to chroot into, then run grub-install from there. > > When grub asks where to install, you should configure it for both sda > and sdb. I think 'dpkg-reconfigure grub-pc' is where that is > selected. Might need it to use -plow to asks all levels of questions. > Not sure. +1 for this suggestion. This is definitely the way to go to fix your problem. Francesco Pietra wrote: > In my case, with the sda that contained grub loader replaced by a new > disk, the rescue mode (using the same CD installer for amd64 wheezy) > did not find any partition. Inverting the SATA cables, same result. No partitions at all? That is scary. And I find it to be hard to believe. No partitions would mean that the data from your disks were zeroed out. Perhaps you were mistaken? Please try it again. > In both cases (I mean position of SATA cables) I went to the shell in > the installer environment: Don't work from the installer environment. Work from the target environment. That is a critical difference! > #fisk /dev/sda (or sdb) "fisk"? That command does not exist in the installer environment. You must have been elsewhere. > device contains neither a valid DOS partition table, nor Sun, etc > (expected for a raid) Try 'cat /proc/partitions' for a simple safe read-only start. > #dmesg |grep -i sd > sda (and sbb): unknown partition table (expected for a raid), however > md: raid0 > md: raid1 > were identified, along with rai4, 5, 6 etc (unfortunately "| less" > does not work to see the whole message). > > Am I using the Rescue Mode improperly? I was unable to dig into the HD > that contains md0 (booth loader, EXT2) and md1 ( LVM partitions home > tmp usr opt var swap EXT3) I believe you are using rescue mode improperly. I have written about how to use rescue mode several times recently. Here is one posting: http://lists.debian.org/debian-user/2013/01/msg00218.html Here is the official documentation for it: http://www.debian.org/releases/stable/i386/ch08s07.html.en But that is fairly terse. Let me say that the rescue mode looks just like the install mode initially. It will ask you keyboard and locale questions and you might wonder if you are rescuing or installing! But it will have "Rescue" in the upper left corner so that you can tell that you are not in install mode and be assured. Get the tool set up with keyboard, locale, timezone, and similar and eventually it will give you a menu with a list of actions. Here is a quick run-through. Advanced options... Rescue mode keyboard dialog ...starts networking... hostname dialog domainname dialog ...apt update release files... ...loading additional components, Retrieving udebs... ...detecting disks... Then eventually it will get to a menu "Enter rescue mode" that will ask what device to use as a root file system. It will list the partitions that it has automatically detected. One of the menu entry items near the bottom will be "Assemble RAID array". That will bring up the next dialog menu asking for partitions to assemble. Select the appropriate for your system. Then continue. Since at this point you have one disk with data and one disk without it means you must assemble a degraded array with only one disk. Select the disk with your data on it. Start the array with that one disk. If you used LVM (I always do) then that should produce an additional set of listings for the lvm volumes on your system including the root logical volume. Select it. At that point it presents a menu "Execute a shell in /dev/...". That should get you a shell on your system with the array mounted. You should 'cat /proc/mdstat' and verify that you have a degraded array with one disk. If you replaced sda with a new sda disk then sdb will contain your data. Assuming sdb1 for md0 and sdb5 for md1 would produce the need for these commands. Adjust those partitions as needed to match your case. Examine the arrays. Assuming md0 is on your sdb1 then: mdadm --detail /dev/md0 mdadm --examine /dev/sdb1 At that point I would do nothing before sync'ing the array to the new disk. If you have multiple arrays then sync each of them. Adjust these partition names as appropriate for your case as determined by the above inspection. mdadm --manage /dev/md0 --add /dev/sdb1 mdadm --manage /dev/md1 --add /dev/sdb5 mdadm --manage /dev/md2 ... and so forth If you have /boot on a separate partition then I would let it finish before installing grub. Or if it is on the main root partition then I would let the entire root partition containing /boot finish syncing before installing grub. Install grub to both disks. You said Wheezy. The way to install grub 2 in wheezy is: grub-install /dev/sda grub-install /dev/sdb That will individually install grub to the MBR of each of the disks. Should work. I test this by booting each disk individually to the grub menu screen. (If you boot past to the kernel on an individual disk then it will dirty the array and require a sync again to make the mirror clean again. Booting to the grub menu is usually sufficient to test that each disk can individually boot.) I have done this above technique for real many times and the rescue media works very well for it. Bob
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