Queue Depth and vSCSI controllers We have a purestorage san, a couple of VMhosts each serving up several SQL Server VM's. Each VMhost is given a slice of the SAN and each SQL Server VM is presented a single data VMDK and a single log VMDK. 

Some SQL Servers have like 50+ databases. Each SQL Server VM is presented 1 single vSCSI controller. 

Can adding a second vSCSI and creating another drive improve performance by increasing Queue Depth?
Ensure you read the VMware / SQL Server best practices guidelines.

This is taken from that document:


  Utilize the VMware Paravirtualized SCSI (PVSCSI) Controller as the virtual SCSI 
  Controller for data and log VMDKs. The PVSCSI Controller is the optimal SCSI 
  controller for an I/O-intensive application on vSphere allowing not only a higher I/O 
  rate but also lowering CPU consumption compared with the LSI Logic SAS. In addition, 
  the PVSCSI adapters provide higher queue depth, increasing I/O bandwidth for the 
  virtualized workload. 
  
  Use multiple PVSCSI adapters. VMware supports up to four (4) adapters per a VM and 
  as many as necessary, up to this limit, should be leveraged. Placing OS, data, and 
  transaction logs onto a separate vSCSI adapter optimizes I/O by distributing load 
  across multiple target devices and allowing for more queues on the OS level. Consider 
  distributing disks between controllers. vSphere 6.7 supports up to 64 disks per 
  controller


VMDK disk files have their own queue, with 64 entries, by default.  PVSCSI adapters have a default queue length of 256 per PVSCSI adapter, however those settings can be modified.