Tim On Computer Science

To set up your USB Flash drives as pass-through in VirtualBox, here is what you can do.

Next, plug in your flash drive and record its device. For me, it was /dev/sde. Look in /var/log/syslog, or dmesg output, for the “[sde] Attached SCSI removable disk” line. My device looked like this:

ls -l /dev/sde
brw-rw---- 1 root disk 8, 64 Nov 24 15:22 /dev/sde

If you don’t run virtualbox as root (and you should not), then you’ll need to use the group to access /dev/sde. Above, you can see it is “disk”.
Now, make sure the user that is running virtualbox is in the “disk” group (e.g. ‘tim’ user):

sudo usermod -a G disk tim

After this, you may or may not have to reboot. Run “groups” as your user. Make sure you see “disk” listed. If not, reboot (or maybe just logout and login).

Then, for each USB Flash drive, run this VBoxManage command:
(Note: this command just creates a *.vmdk file that “links” to a raw device. It does not touch or alter the device, but it does make sure your current user has permissions to the device):

VBoxManage internalcommands createrawvmdk -filename usbflash1.vmdk -rawdisk /dev/sde1
chown tim:tim usbflash1.vmdk

Then, in the virtualbox GUI, under settings, choose Storage, then “add hard disk”, then “Choose existing disk”, then select the usbflash1.vmdk file created above.

See the ZFS Fkash Drives on how to create your ZFS volume from the USB Flash drive(s).

Next up: plugging the USB Flash drives into a different ZFS instance.
(In case it is not clear, the trade-off here is between:
1) Two separate USB flash drives, which can be used by just about any computer, but must be manually kept in sync, and manually compared looking for differences, versus
2) Two flash drives as a single ZFS mirror volume, where ZFS makes sure the contents are the same and scrubs them to make sure they stay that way. However, you need a ZFS system to mount and use them.)

The contents of usbflash1.vmdk:

# Disk DescriptorFile
version=1
CID=1d3a8b59
parentCID=ffffffff
createType="fullDevice"

# Extent description
RW 15130017 FLAT "/dev/sde1" 0

# The disk Data Base 
#DDB

ddb.virtualHWVersion = "4"
ddb.adapterType="ide"
ddb.geometry.cylinders="15009"
ddb.geometry.heads="16"
ddb.geometry.sectors="63"
ddb.uuid.image="33234751-eccf-4188-8e3d-a903b8a4ad74"
ddb.uuid.parent="00000000-0000-0000-0000-000000000000"
ddb.uuid.modification="ee7f3673-388e-42ab-9fa6-698cd80fb5bd"
ddb.uuid.parentmodification="00000000-0000-0000-0000-000000000000"
ddb.geometry.biosCylinders="941"
ddb.geometry.biosHeads="255"
ddb.geometry.biosSectors="63"

As an experiment, I created a small (8GB) ZFS volume in a mirror configuration using two 8GB USB Flash drives.

The purpose was to put “small, but really important things” on this storage system.

It actually ended up being two discrete pieces of work. First, setting up a VirtualBox FreeNas 9 image with “USB passthrough”. Second, running the FreeNas/BSD commands to create the volume by hand, since FreeNas insists on using 2G (fixed) per disk when it creates volumes. 2GB of 1000GB isn’t even a drip; 2GB of 8GB is significant.

So, second things first: creating the partition and volume and getting FreeNas to acknowledge it.

Once you know the two devices in FreeNas (for me it was /dev/ada1 and /dev/ada2), you can run these commands:

gpart create -s gpt /dev/ada1

gpart add -i 1 -t freebsd-zfs /dev/ada1
# now run ls -l /dev/gptid, make note of the new entry,
#   e.g.  d50a7a3b-aeb0-11e6-86a2-080027bed2b8

gpart add -i 1 -t freebsd-zfs /dev/ada2
# make note of that gptid too, 
#    e.g.  e9c860e9-aeb0-11e6-86a2-080027bed2b8

Since my two USB drives were not exactly the same (7.4G versus 7.2G), the zpool create required the “-f” flag:

zpool create -f  usb8 mirror /dev/gptid/d50a7a3b-aeb0-11e6-86a2-080027bed2b8 /dev/gptid/e9c860e9-aeb0-11e6-86a2-080027bed2b8

zpool status
  pool: usb8
 state: ONLINE      
  scan: none requested 
config:   
        NAME                                            STATE     READ WRITE CKSUM  
        usb8                                            ONLINE       0     0     0 
          mirror-0                                      ONLINE       0     0     0    
            gptid/d50a7a3b-aeb0-11e6-86a2-080027bed2b8  ONLINE       0     0     0 
            gptid/e9c860e9-aeb0-11e6-86a2-080027bed2b8  ONLINE       0     0     0  

Then, to get FreeNas to acknowledge it:

zpool export usb8

Finally, in the FreeNas GUI, run “Import Volume”, no encryption, selecting the volume name in the drop-down list. Under “Disks”, you should see two “7.xGiB” entries, not the “5.xGiB” the the 2GB swap partition would have given you.

If you didn’t make note of the gptid as you created the partitions, you can run

gpart list

And look for the “Name: ada1p1” entry to get the “rawuuid” value to use with /dev/gptid/hxhxhx….

Using the gptid/rawuuid, instead of /dev/adaX, is a good idea in general. In this particular case, remember that the device is actually a VirtualBox-created “Disk”, with a VirtualBox serial number, and a VirtualBox gptid.

See the next post on how the “pass-through” was created in VirtualBox.