Ubuntu: Warning: The Partition is misaligned by XXX - Revisiting this question


I know this has been addressed, but I still have a question:

I recently bought a WD 4TB Green hard drive to use as one of my data backups. I made a single partition using GUID instead of MBR. My GUI version of Dist Utility that came with my version of Linux Ubuntu 12.04LTS) is reporting the partition misalignment by 3072 bytes.

My reading on the forums seems to indicate that if I used GUID partitioning, I don't need to worry about the partition misalignment, that it's irrelevant. Obviously, I don't know much about what I'm doing with disk partitioning and formatting, and I don't know much more about Linux, other than it's been an exceptional OS for my needs.

Anyway, I am hoping that someone with more knowledge and experience can comment and tell me if the above assumption is correct, or if I need to go back and re-align the partition.


You should identify the sector-precise start point of the partition. You can do this in GParted by selecting your disk's one partition, right-clicking, and selecting "Information" from the pop-up menu. This produces a dialog box like the following:

GParted's Information dialog box

The "First sector" line tells you what the first sector is.

Alternatively, typing sudo parted /dev/sda unit s print or sudo gdisk -l /dev/sda should produce the same information. (gdisk isn't installed by default, though; you'll need to install it first via sudo apt-get install gdisk).

In any of these cases, if the first sector value is divisible by 8, you're safe. If not, the partition is misaligned and you should back it up, delete it, re-create it, and restore the data. Doing a move/resize operation on the start of the disk should also correct the problem; but be aware that this is risky, so backing up is advisable in this case.

Note that the partition shown in my screen shot is not properly aligned. This is OK in my case because the disk is not an Advanced Format model. Proper alignment is required only for Advanced Format disks, SSDs, and some types of RAID arrays; but precisely what type of alignment is necessary depends on the disk type. The vast majority of modern spinning disks use Advanced Format, so it's best to assume you need to align on 8-sector boundaries with any modern hard disk.

For more on this topic, see this article, which I wrote some time ago. Modern software is a bit better at this than it was in 2010, but you can still wind up with improper alignment if you use old software, if you use unusual software, or if you mis-use advanced partitioning options that override alignment defaults. Alignment issues are mostly the same for MBR as for GPT disks.

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