Can I resize a filesystem without resizing the partion in advance?

Question

Quick question: Can I resize a filesystem without resizing the partition in advance? The question aims at growing, but information on shrinking might be useful for future reference too.

Here's the scenario:

• SLES VM running on vSphere
• Extend virtual disk to bigger size
• The disk has a single partition but no LVM
• Log into SLES VM and run the following commands:
  • Perform SCSI rescan: echo '1' > /sys/class/scsi_disk/<foobar>/device/rescan
  • Verify extended disk: fdisk -l
  • Resize filesystem: resize2fs /dev/foo
• Result: Filesystem successfully resized

A colleague told me about this and did it, but I was sure that it have to resize the partition with fdisk or similar in advance as pointed out here.

Answer 1

You can (and should) certainly shrink a filesystem before shrinking the partition, though not necessarily - if you shrink the partition first, unless you create a new partition, nothing should write to the new empty space, but it still feels dangerous.

If you are talking about growing the filesystem, you can overwrite some space following the partition (e.g. with superblock copies). Again, it could work if nothing writes to the (officially) empty space before resizing the filesystem, but resize2fs will normally not grow beyond the size of the partition.

Note that your example looks like resizing the whole disk and using the filesystem in partitionless mode. In that case, shrinking the disk size before the filesystem might (and likely will) result in filesystem corruption, while growing the filesystem has to be done after you extend the disk size.