So some of the documentation I see in various places either recommends to umount or doesn't even talk about it when adding space to a partition that falls under LVM.

I know to backup the data, however I'm wondering what others think here. Do you umount an LVM partition before growing it or do you even bother with that?

thanks

LVs and the filesystems on them can safely be extended online with no problems. (There's always the possibility some issue that hasn't bit you yet bites you when you do an extension which is why you want a backup but it is extremely rare.) I've done extensions of lvm2 for years with no issues mostly on ext2/ext3/ext4 filesystems.

Where you DO want to umount is if you're shrinking an LV and underlying filesystem. Some filesystems tell you they can sometimes shrink on line with no ill effects but your likelihood of something going wrong to a reduction is quite a bit higher. Some filesystems such as XFS don't even allow filesystem shrinking.

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Good info.

I've only worked with ext3/ext4 in production when it comes to LVM.

Started to lab with xfs when it comes to LVM. Seems a little more restrictive. Surely there is a reason for it.

The devs for enterprise tools seems to presume everyone will only ever want to extend. The original LVM suffered from this same short-sightedness. Took years to correct. ZFS fanboys keep pontificating about no need for a simple means to reduce a zpool as well.
They all (and XFS devs) need a kick in the arse - simple as that IMHO.

Use a filesystem that does what you need - btrfs in my case, but ext4 is also fine.

Well I have yet to lvreduce, vgreduce or pvresize. We are always needing more space...

On occasion I've had to do reduction but not very often. It usually occurs when we've done initial layout using all space of internal disks and have no SAN attachments to the server. If one filesystem is using more space than originally planned for and another has a fair amount free it makes sense to reduce the one with the free space to expand the one that needs more.