I don’t know if this is the right place to post this but I’ve had a series of problems with my external HDD that I think may be worth reporting. The first problem I encountered was that the ext drive prevented me from installing Ubuntu Mate 16.04 (Problems with installing Ubuntu Mate 16.04 beta2 - help please!). More recently I encountered another two types of bugs/ problems related to the ext drive. During boot-up and with the drive connected I get a wall of errors “Error: cannot access /dev/sbg”. The HDD does mount however and works fine once the system starts. But the boot takes considerably longer (20-30s longer I reckon) – I guess that this is caused by the errors. A more severe problem I encountered is that I cannot change anything in the GRUB settings with the ext HDD connected. If the external drive is connected and I try to change anything in GRUB the system freezes instantly; same goes for using Grub Customiser. I’ve had this drive connected from more than a year and had no problems in 15.10 or windows in the past.
Is it possible that the drive is failing?. 
Thank you for your response. While it is possible that the drive is failing I find it unlikely. As I’ve said I have no problems with the drive when booting into Windows and while using it. I also tried it on my Mac and found that it caused no problems. Anyways, even if it is failing I cannot see how and why it would cause a crash when fiddling with GRUB.
It’s just a storage drive I might add if it wasn’t clear from the post. 
Is the external USB disk bus powered or do you use an external power supply?
What USB bus is the device connected to? Use:
lsusb | sortHave you run S M A R T on the USB disk? You might want to install smartctl:
sudo apt-get install smartmontoolsOnce installed, run: (If the USB drive is still /dev/sdb)
sudo smartctl -Aa /dev/sdbHave you looked at the boot messages to see if the disk is throwing any errors during boot?
dmesg | moreThe ext drive is bus powered.
Bus 005 Device 001
I followed your suggestion and installed smartmontools. No errors.
Did dmesg | more. No errors - all I get in regard to the drive is:
usb 5-1.2: Manufacturer: Inateck
[ 3.639165] usb 5-1.2: SerialNumber: 0123456789ABDFE
[ 3.639619] usb-storage 5-1.2:1.0: USB Mass Storage device detected
[ 3.639741] scsi host9: usb-storage 5-1.2:1.0
[ 3.785006] EXT4-fs (sdf1): mounted filesystem with ordered data mode. Opts: (null)
[ 5.171374] scsi 9:0:0:0: Direct-Access Inateck 5B PQ: 0 ANSI: 6
[ 5.171721] sd 9:0:0:0: Attached scsi generic sg6 type 0
[ 5.172033] sd 9:0:0:0: [sdg] 312581808 512-byte logical blocks: (160 GB/149 GiB)
[ 5.172661] sd 9:0:0:0: [sdg] Write Protect is off
[ 5.172663] sd 9:0:0:0: [sdg] Mode Sense: 43 00 00 00
[ 5.173334] sd 9:0:0:0: [sdg] Write cache: disabled, read cache: enabled, doesn’t support DPO or FUA
[ 5.290013] sdg: sdg1 sdg2
Is bus 5 an USB 3 bus on your system? Normally higher USB buses are USB 1.1.
Is the system a laptop or desktop? Frequently, laptops have very weakly powered USB ports.
How much power does the attached drive need? I don’t see a drive model that I recognize.
Smartctl may not show that the drive is failing but it will show if the drive is in trouble.
For example, here is a drive with seek problems:
ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE
7 Seek_Error_Rate 0x000f 086 060 030 Pre-fail Always - 460181228
195 Hardware_ECC_Recovered 0x001a 085 077 000 Old_age Always - 82418956This particular drive has trouble booting because it gets seek errors getting to all of the files
required to boot. There are no errors in the boot log either.
Thanks. I know very little about USB buses but I double checked and it is clearly listed as bus 5. It is a stationary computer; I dont really know how much power it draws but its a standard 2.5 in drive - which I took out of a dead Macbook and put it in this case: http://www.amazon.co.uk/Inateck-External-Enclosure-Tool-free-Installation/dp/B00DW374W4?ie=UTF8&keywords=inateck%20drive&qid=1460740212&ref_=sr_1_1&sr=8-1
Here is an example of the info needed to help determine your problem:
(My USB to disk adapter)
mybox:~$ lsusb | sort
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 0409:005a NEC Corp. HighSpeed Hub
Bus 001 Device 003: ID 046d:0824 Logitech, Inc.
Bus 001 Device 004: ID 0a12:0001 Cambridge Silicon Radio, Ltd Bluetooth Dongle (HCI mode)
Bus 001 Device 005: ID 0409:005a NEC Corp. HighSpeed Hub
Bus 001 Device 006: ID 06f8:c000 Guillemot Corp. Hercules Muse Pocket
Bus 001 Device 007: ID 152d:2338 JMicron Technology Corp. / JMicron USA Technology Corp. JM20337 Hi-Speed USB to SATA & PATA Combo Bridge
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 003: ID 048d:1336 Integrated Technology Express, Inc. SD/MMC Cardreader
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 002: ID 413c:3010 Dell Computer Corp. Optical Wheel Mouse
Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
mybox:~$ sudo smartctl -i /dev/sdf
smartctl 6.5 2016-01-24 r4214 [x86_64-linux-4.4.0-17-generic] (local build)
Copyright (C) 2002-16, Bruce Allen, Christian Franke, www.smartmontools.org
=== START OF INFORMATION SECTION ===
Model Family: Fujitsu MHV
Device Model: FUJITSU MHV2040AH
Serial Number: NT26T572EA0U
Firmware Version: 00000096
User Capacity: 40,007,761,920 bytes [40.0 GB]
Sector Size: 512 bytes logical/physical
Device is: In smartctl database [for details use: -P show]
ATA Version is: ATA/ATAPI-6 T13/1410D revision 3a
Local Time is: Fri Apr 15 12:57:07 2016 CDT
SMART support is: Available - device has SMART capability.
SMART support is: EnabledTo summarize:
- My adapter is on USB Bus 1, a USB 2.0 port.
- My USB attached disk drive is a FUJITSU MHV2040AH.
Now, looking up specs for the drive, I see -
Power requirements:
Voltage 5 V± 5%
Spin-up 1.0 A max
1.0 A is too much current for my USB ports so I need an external power supply
for the disk drive.