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6. Modifying an Existing Installation

  1. Q: Are linear MD's expandable? Can a new hard-drive/partition be added, and the size of the existing file system expanded?
    A: Miguel de Icaza < miguel@luthien.nuclecu.unam.mx> writes:
    I changed the ext2fs code to be aware of multiple-devices instead of the regular one device per file system assumption. So, when you want to extend a file system, you run a utility program that makes the appropriate changes on the new device (your extra partition) and then you just tell the system to extend the fs using the specified device. You can extend a file system with new devices at system operation time, no need to bring the system down (and whenever I get some extra time, you will be able to remove devices from the ext2 volume set, again without even having to go to single-user mode or any hack like that). You can get the patch for 2.1.x kernel from my web page:
    http://www.nuclecu.unam.mx/~miguel/ext2-volume
  2. Q: Can I add disks to a RAID-5 array?
    A: Currently, (September 1997) no, not without erasing all data. A conversion utility to allow this does not yet exist. The problem is that the actual structure and layout of a RAID-5 array depends on the number of disks in the array. Of course, one can add drives by backing up the array to tape, deleting all data, creating a new array, and restoring from tape.
  3. Q: What would happen to my RAID1/RAID0 sets if I shift one of the drives from being /dev/hdb to /dev/hdc? Because of cabling/case size/stupidity issues, I had to make my RAID sets on the same IDE controller (/dev/hda and /dev/hdb). Now that I've fixed some stuff, I want to move /dev/hdb to /dev/hdc. What would happen if I just change the /etc/mdtab and /etc/raid1.conf files to reflect the new location?
    A: For RAID-0/linear, one must be careful to specify the drives in exactly the same order. Thus, in the above example, if the original config is
    mdadd /dev/md0 /dev/hda /dev/hdb
                
    
    Then the new config *must* be
    mdadd /dev/md0 /dev/hda /dev/hdc
                
    
    For RAID-1/4/5, the drive's ''RAID number'' is stored in its RAID superblock, and therefore the order in which the disks are specified is not important. RAID-0/linear does not have a superblock due to it's older design, and the desire to maintain backwards compatibility with this older design.


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