It has often occurred to me that the fact that a logical volume is not contiguous will make recovery in the face of a partial disaster more difficult. For example, if I happen to lose the logical->physical extent map in the LVM superblock (the single only place this information is kept AFAIK) then I am pretty screwed with respect to getting my filesystems back off the disk. Compared with just losing the partition table from a traditionally partitioned disk, I could use a tool like findsuper and losetup the whole disk with offsets (losetup -o <offset> to retrieve the individual filesystems. This technique would even work with LVM given that I had lost the part of the disk with the extent mapping except that my filesystems are not contiguous if I have extended any of them. So, the question is, has anyone developed a tool to "defragment" a Volume Group so that all of the logical volumes in it are contiguous? On a somewhat related note, what provisions can I take to mitigate the loss of the extent map? I am correct in that only one copy of it exists at the head of a Physical Volume? Can I make a backup of it in any way so that it could be used at a later date to reconstruct logical volumes? As you might have guessed, I have lost a small portion of a 160GB disk, the portion which has the extent mapping for the whole PV and I want to mitigate this problem in the future. b. -- My other computer is your Microsoft Windows server. Brian J. Murrell
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