Occasionally I have to resize partitions on iSCSI or Fiber-Channel attached SAN storage. Both technologies allow you to easily extend the available storage for a host by extending LUNs, or volumes. A common problem after extending the size of the LUN, or volume, is resizing partitions to fill out the new size.
For the most part, I usually fire up PartedMagic and its a snap, even with Fiber-Channel attached enterprise storage. Once the HBA’s have been zoned to Fiber-Channel switches, then the HBAs do all the heavy lifting. In other words on Fiber-Channel, it doesn’t matter if you’re using PartedMagic, or Knoppix, the server just knows where the storage is, and that its certainly attached. The only dependency for this working on a Live boot disk are drivers for the HBA cards.
iSCSI is a bit different. Because, iSCSI relies on commodity Network Interface Cards, this technology is largely implemented in software. One perceived advantage is iSCSI may seem less complicated to use than Fiber-Channel storage. Unfortunately, in this case, PartedMagic did not have open-iscsi software, and I could install open-iscsi in the Knoppix Live ramdisk. However, because Knoppix came with an outdated iSCSI kernel module, it was not new enough to inter-operate with the open-iscsi software.
Furthermore, the version of parted that shipped with RHEL 5 threw an incompatible filesystem error, refusing to modify the filesystem. So, in the end, I twiddled some bits on the partition table with fdisk, and used resize2fs to extend the partition.
Assuming you have a backup of the filesystem you are working on, you can proceed with the following steps to extend a single partition to the end of the extended volume. If you have multiple partitions on a volume, you may want to stick to more reliable methods of resizing and extending. If you screw up the cylinder boundaries on a device with multiple partitions, you’ll definitely lose data. A single partition, in this example, is a much simpler scenario.
The device name in this example is /dev/mapper/u02, the first partition is /dev/mapper/u02p1:
- Runfdisk -l /dev/mapper/u02 to get the starting cylinder.
Disk /dev/mapper/u02: 100.9 GB, 108340550042 bytes
255 heads, 63 sectors/track, 13171 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/mapper/u02p1 1 13171 26450329 83 Linux
- Reboot the server, after extending the volume or LUN on your SAN, and before proceeding to extend the partition in your Operating System. The Operating System needs to re-read sector 0 on the extended SAN volume, before continuing. Note, that fdisk will report 26109 cylinders instead of 13171, after I rebooted the server.
- Next, we will run: fdisk /dev/mapper/u02, and then hit the keys: d, n, p, 1, [enter], [enter], w
WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
switch off the mode (command 'c') and change display units to
sectors (command 'u').
Command (m for help): d
Selected partition 1
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-26109, default 1):
Using default value 1
Last cylinder, +cylinders or +size{K,M,G} (1-26109, default 26109):
Using default value 26109
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
- Finally, run resize2fs on /dev/mapper/u02p1. If you are using ext3, you can do an on-line resize while the volume is mounted. It is probably safest to umount the partition to be re-sized, however.
resize2fs 1.39 (29-May-2006)
Filesystem at /dev/mapper/u02p1 is mounted on /u02; on-line resizing required
Performing an on-line resize of /dev/mapper/u02p1 to 52430127 (4k) blocks.
The filesystem on /dev/mapper/u02p1 is now 52430127 blocks long.Refer to the resize2fs for more information on the command, and its proper usage.
