When working with ESXi virtualization, administrators often need to attach external storage directly to VMs while bypassing the hypervisor's storage management. This becomes crucial when:

• Migrating physical file servers to virtual environments
• Needing portable storage that maintains file system integrity
• Avoiding vSAN or datastore overhead for temporary storage

ESXi offers several methods to achieve direct USB storage access for VMs:

# Check connected USB devices on ESXi host
esxcli storage core device list | grep -i usb

# Alternative method using lsusb equivalent
esxcfg-scsidevs -l | grep -i "usb"

While technically possible, RDM isn't ideal for USB devices because:

• USB storage appears as /vmfs/devices/disks/ but lacks persistence
• Device paths change after host reboots
• Requires manual VM configuration file edits

The most reliable approach involves PCI passthrough of the USB controller:

# Identify USB controller hardware address
lsusb -v | grep -i "controller"

# Enable passthrough in ESXi host configuration
esxcli system module list | grep -i usb
esxcli system module parameters set -m vmwusb -p "enablePassthrough=1"

1. Power off the target VM
2. Navigate to Host > Manage > Hardware > PCI Devices
3. Find your USB controller (typically shows as xHCI)
4. Toggle passthrough and reboot the host
5. Edit VM settings > Add Other Device > PCI Device

Problem: Device not persisting after VM reboot
Solution: Add these lines to VMX configuration:

usb.present = "true"
usb.generic.allowHID = "true"
usb.port.poweroff = "false"

For environments where passthrough isn't feasible:

# On Linux guest example:
modprobe usbip-core
modprobe usbip-host
usbipd -D
usbip bind -b $(lsusb | grep -i "yourdevice" | cut -d' ' -f2,4 | tr ' ' '.')

Benchmarking shows USB 3.0 passthrough delivers:

• ~400MB/s sequential read (comparable to bare metal)
• ~5% overhead compared to direct host attachment
• Latency spikes during ESXi storage operations

When ready to transition to permanent storage:

# Example rsync command for Linux VMs
rsync -ahv --progress /mnt/usbstorage/ user@newserver:/data/

When working with VMware ESXi (particularly version 4.0 and later), administrators often need to expand VM storage without committing to permanent SAN/NAS solutions. The core requirement here is achieving direct device passthrough to a specific VM, bypassing ESXi's storage management layer for maximum portability.

Before implementation, verify:

1. ESXi host detects the USB controller via:
   # lsusb -v | grep -i "mass storage"
2. The VM supports USB controllers (check VM hardware version)
3. vSphere Client/Web Client access

Method 1: Raw Device Mapping (RDM)

While not ideal for USB, this maintains some ESXi visibility:

# Identify the USB device UUID
esxcli storage core device list | grep -A10 "USB_Device"

# Create RDM mapping
vmkfstools -z /vmfs/devices/disks/ /vmfs/volumes/datastore1/usb_rdm.vmdk

Method 2: Direct PCI Passthrough (Recommended)

For true hardware-level access:

1. Enable PCI passthrough in ESXi host:
   - Navigate to Host > Configure > Hardware > PCI Devices
   - Enable passthrough for relevant USB controller
2. Add PCI device to VM:
   - Edit VM settings > Add PCI Device

After attaching the storage:

# Inside guest OS (Linux example):
dmesg | grep -i usb
lsblk  # Verify disk detection

# Windows guests should show new disk in Disk Management

• USB 3.0 controllers generally work better than USB 2.0 for this purpose
• Always safely eject drives before physical removal
• Performance will be limited by USB bus speeds (consider eSATA alternatives)

Scenario: VM fails to start after PCI passthrough configuration

# Check host logs:
tail -f /var/log/vmkernel.log | grep -i "usb"
# Common fixes:
- Disable memory hot-add for the VM
- Ensure no other VMs are using the controller