One thing that has always perplexed me is storage best practices. Filesystems brag about how they can be petabytes or exabytes in size. Yet, I do not know many sysadmins who are willing to let a single volume grow over several terrabytes. I do know the primary reason behind this is how long it would take to rebuild the array should a drive fail. The more drives in a single LUN, the longer this takes and the greater your risk of losing another drive while the rebuild is taking place.

Then there's usage reasons. Admins will carve out a LUN based on how much space they think needs to be allocated to the project. It seems more practical to me for the LUN to be one large array and to use quotas. I understand this wouldn't satisfy every requirement (iSCSI), but I see a lot of NAS systems (NFS) managed this way. I also understand that the underlying volumes can be grown/shrunk as needed quite easily, but wouldn't it be less "risky" to use quotas rather than manipulating volumes and bringing possible data loss into the equation?

There may be some other reasons I'm missing, so please enlighten me. Can we not expect filesystems to ever be so large? Are we waiting for the hardware to get faster to cut down on rebuild times?