It seems I can't mount 4k sector size msdos disks. I don't know if the underlying FS is 4k or 512 byte sectors; I just know that this USB enclosure works fine on Linux, Windows and MacOS X. However, under FreeBSD: usb_alloc_device: set address 2 failed (USB_ERR_IOERROR, ignored) usbd_setup_device_desc: getting device descriptor at addr 2 failed, USB_ERR_IOERROR usbd_req_re_enumerate: addr=2, set address failed! (USB_ERR_IOERROR, ignored) usbd_setup_device_desc: getting device descriptor at addr 2 failed, USB_ERR_IOERROR ugen4.2: <iomega> at usbus4 umass0: <Mass Storage Class Interface> on usbus4 umass0: SCSI over Bulk-Only; quirks = 0x0000 umass0:2:0: Attached to scbus2 da0 at umass-sim0 bus 0 scbus2 target 0 lun 0 da0: <OEM Ext Hard Disk 0000> Fixed Direct Access SCSI-5 device da0: Serial Number 0000D20313BC da0: 1.000MB/s transfers da0: 476240MB (121917446 4096 byte sectors: 255H 63S/T 7589C) da0: quirks=0x2<NO_6_BYTE> cd1 at umass-sim0 bus 0 scbus2 target 0 lun 1 cd1: <Virtual CDROM > Fixed CD-ROM SCSI-0 device cd1: 1.000MB/s transfers cd1: cd present [358400 x 2048 byte records] cd1: quirks=0x10<10_BYTE_ONLY> root@lucy-11i386:~ # .. then: root@lucy-11i386:~ # fdisk da0 fdisk: could not detect sector size root@lucy-11i386:~ # gpart list da0 Geom name: da0 modified: false state: OK fwheads: 255 fwsectors: 63 last: 121917445 first: 1 entries: 4 scheme: MBR Providers: 1. Name: da0s1 Mediasize: 499373850624 (465G) Sectorsize: 4096 Stripesize: 0 Stripeoffset: 8192 Mode: r0w0e0 rawtype: 11 length: 499373850624 offset: 8192 type: fat32 index: 1 end: 121917445 start: 2 Consumers: 1. Name: da0 Mediasize: 499373858816 (465G) Sectorsize: 4096 Mode: r0w0e0 .. so: root@lucy-11i386:~ # mount -t msdosfs -o large /dev/da0s1 /mnt mount_msdosfs: /dev/da0s1: Invalid argument This is on: adrian@lucy-11i386:~/work/freebsd/head/src/sys/fs/msdosfs % uname -a FreeBSD lucy-11i386 11.0-CURRENT FreeBSD 11.0-CURRENT #0 r276053M: Mon Dec 22 00:44:47 PST 2014 adrian@lucy-11i386:/usr/home/adrian/work/freebsd/head/obj/usr/home/adrian/work/freebsd/head/src/sys/LUCY_11_i386 i386