Partitions Over 2.1 TB

Introduction

As hard drives have increased in capacity over time, some clever workarounds have been engineered to keep breaking barriers, such as the move from CHS to LBA. Unfortunately, with older style MBR partitions, there is a limit of 2.1TB that simply cannot be worked around using an MBR partition. We have to instead use newer GPT style partitions.

I'm not going to delve into the history too much, you can google/wikipedia it yourself if you like.

So, if you've just purchased a snazzy new 3TB drive like a Western Digital Caviar Green, and you're scratching your head as to why you can't get the full capacity, here's the fix.

Assumptions

The below documentation assumes you have an existing boot drive with Amahi, namely /dev/sda. Your >2.1TB HDD will be /dev/sdb

The instructions also assume a Linux terminal, such as that on your Amahi box (either using its console, the Terminal application within the GUI, or SSH'd in)

Warning

BE ABSOLUTELY SURE THAT YOU ARE RUNNING THESE COMMANDS AGAINST THE CORRECT DRIVE. I ACCEPT NO RESPONSIBILITY FOR ANY DATA LOSS ETC!

OK, Let's do it

First we label the drive with a GPT partition

bash code
​ parted /dev/sdb mklabel gpt ​

Now we select sectors as a unit of measurement

bash code
​ parted /dev/sdb unit s ​

Now we make the partition.

bash code
​ parted /dev/sdb mkpart primary ext2 2048 -1 ​

Parted may complain about the last sector and will automatically suggest a correct sector, just say Yes to the prompt.

We make it as a primary partition, ext2 filesystem, and we carefully select the sectors. The first number MUST be divisible by 8, so you can try 40, 48, 56, 64 etc... For me these numbers threw up errors, so I just went to 2048 and everything worked fine, and in the grand scheme of a 3TB drive, the extra sectors don't really matter :)

The reason that the starting sector is divisible by 8 is for aligning the sectors. This is because HDD's have traditionally been based around 512-byte sectors, yet newer, higher capacity HDD's are now arriving based around 4096-byte (a.k.a. 4k) sectors. The partitioning will still work with 512-bytes, but the drive's performance will be drastically impacted - in some testing it can be twice as slow, in others up to 25 times slower, depending on the sector alignment. So it's important to get this right!!!

Alternative Parted usage

Instead of the sequence of one liners up there, you can enter into parted itself like this. I give this as I don't know how your version of parted is going to behave. The interactive stuff from parted has been removed:

bash code
​ parted /dev/sdb (parted) mklabel gpt (parted) unit s (parted) mkpart primary ext2 2048 -1 (parted) quit ​

Format the drive!

Finally, let's get that drive formatted to a nice ext4 volume:

bash code
​ mkfs.ext4 -T largefile4 /dev/sdb1 ​

A note about Western Digital drives

Western Digital make some nice hardware, but they are also incredibly stupid. Many of their hard drives will automatically park their heads every 8 seconds, which wears out the hard drives very quickly, in some cases the HDD's will reach their design limit (300k parks for consumer, 600k parks for enterprise) within 3-4 months!!! This isn't to say that the drives will necessarily die within 3-4 months, but it's still not good!

Fortunately we can fix this using a Western Digital tool named wdidle3. You can download it here.

Create a bootable usb drive using FreeDOS and unetbootin, then copy wdidle.exe onto the usb drive. Boot up your Amahi box to FreeDOS and enter the following commands:

bash code
​ c:\ wdidle3 /R wdidle3 /S300 ​

This cd's you to the usb drive's root, then we run wdidle3 /R to display the current drive status, then we run wdidle3 /S300 to set the park time to 5 minutes. Alternatively you could run wdidle3 /D to completely disable the parking.

When you're done, simply restart the PC!

n.b. Unetbootin was a bit finnicky for me, I found that if I created the drive with a FreeDOS live CD that it wouldn't work, but if I then re-created using unetbootin's automatic distribution download feature, the USB stick worked a treat. YMMV.