Right, after reading the link I recalled that this was implemented for Direct SAN Access transport mode (just as per the User Guide's section), so this is the correct setting for that case.mkretzer wrote: ↑Aug 06, 2019 4:24 pmhttps://helpcenter.veeam.com/docs/backu ... l?ver=95u4
"Veeam Backup & Replication automatically sets the SAN Policy within each proxy to Offline Shared."
But I also stand corrected that offlineShared is a cause of the issue for hot add. After digging Microsoft documentation on SAN policies, this setting does appear to cover SCSI bus disks too (and not just iSCSI, as I thought). So, my idea was completely incorrect... back to drawing board.
Right now I am completely lost as to why "half of our volumes get mounted on the proxy (including getting a drive letter) while backup is running"... all possible ideas are now proven 100% wrong. Due to offlineShared setting, they should have been kept offline and read-only.