@floh8:
- TrueNAS Enterprise
- PetaSAN
- Lustre
- Blockbridge
- LinStor
- StarWind
- Nexenta
- HoustonUI
Not to talk about the hundreds of other shared storage options over NFS, iSCSI, NVMeoF. I think you don't realize what you're asking for when you want synchronously replicated, shared storage, you can think through it quite simple:
- set up two iSCSI targets on two different system, RAID1 them in your OS.
- what happens when one of your nodes goes down, it comes back, the other goes down before the replication is finished
That is what you're asking for. Replication is always snapshot-based, asynchronous and you can never automatically engage an asynchronous replica without someone guaranteeing that your original storage is dead and you are ready to accept the data loss.
If you want shared storage over iSCSI, you can do that with Proxmox today - set up an LXC container or VM (eg. TrueNAS) that shares out iSCSI of a shared fabric (SAS, FibreChannel, Ethernet etc), set up HA, whenever a node goes down, the system starts itself on another node and imports the pool. This is exactly how TrueNAS Enterprise, Nexenta etc works.
The market really is rife with options and many of the above are free or have community editions. Not to speak that the tools to build this are built-in to every major Linux distro.