What is your storage configuration? Is this an iSCSI storage? If so, is the "Use LUN directly" option enabled?
In most cases, when you export one large LUN you would disable that option and create an LVM with the "shared" option enabled on top of that LUN.
And if you have multiple connections to the iSCSI, you should also configure multipathing to make it redundant:
https://pve.proxmox.com/wiki/Multipath