Questions about possible issues with multiple servers accessing the same iSCSI target to NTFS or ReFS formatted volume are often discussed among people who run applications that are already highly available by design and do not need Microsoft Failover Cluster but still need some shared storage and preferably a highly available one.
Letting multiple hosts use the same LUN formatted as NTFS or ReFS filesystem connected as a local disk over iSCSI will most probably lead to all manners of problems, including data corruption.
The reason is that iSCSI protocol itself does not do anything in the way of file locking. It is a block-level protocol that allows storage data transmission over the network and does not know what a file is. You can think of it like pure Ethernet that doesn’t know what SMB is since it’s the job of higher level protocols. Ethernet’s job is just to carry the data encapsulated inside Ethernet packets and then hand it off to connected devices for further processing. You can think of iSCSI as a delivery courier. He does not know what is in the parcel and just delivers it to you. Unless he is an unscrupulous employee. Obviously, letting iSCSI handle file locking would be like asking the courier to assemble delivered new hardware for your home lab. Imagine regular SCSI drives, you can’t just plug them into multiple servers at the same time. It doesn’t work that way. iSCSI along with Fibre Channel and ATA-over-Ethernet are not “sharing” protocols but just a method of remotely accessing a locally attached storage.
The only two ways of properly accessing the same volume from multiple servers are either file level access protocol like SMB 3.0 and NFS or cluster file system like Standard Cluster Disks or Cluster Shared Volumes. In order to convert your existing LUN into a clustered one, you will clearly need to join all the servers into the same cluster and convert your iSCSI connected storage into a Cluster Disk or Cluster Shared Volume.
Another option is to use Microsoft File Server role and convert your iSCSI connected storage into an SMB 3.0 or NFS share.
