Resizing an iSCSI EXT3 disk, partition, and file system

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Category: Linux stuff

A client of mine uses an iSCSI target to back up databases on Oracle Enterprise Linux production machines.

Great concept - until the disk runs out of space and the admins want to take down the server to fix that. Ahum? Take the server offline for a backup drive? Come on, there's got to be a better way. And there is.

The admins' way was:

  1. create a new iSCSI target and connect to it
  2. move the data from the old mounted drive to the new one
  3. mount the new drive as /u04

That took ages (moving a few TB just takes a while - especially if the iSCSI target is a not-overl;y-fast device... it's for backups, you know, so why spend the money)

I figured there had to be a faster way. And there is (we'll use /dev/sdc1 with /u04 as mount point in our example):

  1. unmount the iSCSI device: 
    > umount /u04

  2. turn off journalling on the partition, making it a ext2 partition
    > tune2fs -O ^has_journal /dev/sdc1

  3. disconnect from it
    > iscsiadm -m node -T <iscsi target path> -p <iscsi host> --logout
  4. resize the target on the target system (ie. in the SAN console)

  5. log back into the iscsi target
    > iscsiadm -m node -T <iscsi target path> -p <iscsi host> --login

  6. use fdisk to delete and recreate the partition table (scary, I know)
    > fdisk /dev/sdc
    Command (m for help): p
    => write down start- and end-cylinder of the existing partition
    => now delete the partition (1, in our case):

    Command (m for help): d
    Partition number (1-5): 1

    => Now we re-create the partition (phew!)
    Command (m for help): n
    Command action
       l   logical (5 or over)
       p   primary partition (1-4)
    p
    Partition number (1-4): 1

    First cylinder (1-32267, default 1): 1
    => take the first cylinder from what your wrote down. Most likely it'll be "1"

    Last cylinder or +size or +sizeM or +sizeK (1-32268, default 32268): 32268
    => depends on what you want, but usually you'll want the default here (largest)

    Now make sure that you set up the right things:

    Command (m for help): p

    Command (m for help): p

    Disk /dev/sdc: 268.7 GB, 268703891456 bytes
    255 heads, 63 sectors/track, 32668 cylinders
    Units = cylinders of 16065 * 512 = 8225280 bytes

    Device Boot Start End Blocks Id System
    /dev/sdc1 1 32668 262405678+ 83 Linux

    Looking good? Then write the partition table changes to disk.

    Command (m for help): w
    The partition table has been altered!

    FDisk will complain about the re-reading the table, but we'll work around that in a minute so we don't need a reboot (that WAS the objective right?!)

  7.  Repeat steps 3 and 5 (the --logout / --login steps) to get the disk re-read

  8.  Run fsck to check the filesystem for errors (needs to be done)
    > fsck -n /dev/sdc1

  9. use resize2fs to resize the partition's file system
    >resize2fs /dev/sdc1

  10. turn journalling back on
    >tune2fs -j /dev/sdc1
  11. pray
    >Root Admin, whou thou art at the keyboard, protect this humble consultant's butt, etc etc
  12. mount the partition (we're lazy, so we'll do a -a)
    >mount -a

 Admittedly - a lot more steps, but without the moving of data, it's a heck of a lot faster.