1) unless you are using LVM2 ..the answer is no ..have to umount the file system to extend it.

2) are you using PowerPath ? If yes ..power devices will remain persistent while /dev/sd* may change.

The resize2fs program will resize ext2 or ext3 file systems. It can be used to enlarge or shrink an unmounted file system located on device. If the filesystem is mounted, it can be used to expand the size of the mounted filesystem, assuming the kernel supports on-line resizing. (Linux 2.6 kernel supports on-line resize for filesystems mounted using ext3 only.).
The size parameter specifies the requested new size of the filesystem. If no units are specified, the units of the size parameter shall be the filesystem blocksize of the filesystem.
The resize2fs program does not manipulate the size of partitions. If you wish to enlarge a filesystem, you must first make sure you can expand the size of the underlying partition first.
This can be done using fdisk by deleting the partition and recreating it with a larger size or using lvextend, if you're using the logical volume manager lvm
. When recreating the partition, make sure you create it with the same starting disk cylinder as before! Otherwise, the resize operation will certainly not work, and you may lose your entire filesystem.

After running fdisk, run resize2fs to resize the ext2 filesystem to use all of the space in the newly enlarged partition.

For the lun id question is better to have no gap because if you using the native device at the reboot the linux will change the device id .

This not happen if you use logical volume manager or powerpath device (powerdevice)

Regards
Pierluca

u can extend FS online using ext2online. Most of the time resize2fs fails to do the job at least with RHEL AS 4.

But here the question is NOT about FS extend rather LUN expand. I have a doc which explains the LUN extend on same platform with NetApp. So i guess EMC should work too. But i have not done LUN expand myself.

Can you provide the link to the document you have ?

Thanks
Pierluca

now.netapp.com

Once logged in search for LINUX LUN resize. The first document in the list.