installer: confusion about partition sizes (1000 vs. 1024 issue)

[Sascha Silbe]

If I enter "64m" as the size of the partition to be created, it will correctly create a 64MB (MB=1024^2 bytes, "real MB") partition. But in the partition list it gets displayed as "65.8 MB" (MB=1000^2, "salesman MB"). This is confusing.

Please use 1024-based sizes, since it's what administrators are used to and what resembles the internal structure (512Byte sectors, n-bit block addressing) best. 1000-based sizes are mostly a creation of "marketing experts" to make the devices seem larger than they really are.
A note about this difference in the partition manager could inform novice users why their HD is smaller than expected.

[Colin Watson (cjwatson)]

partman has always behaved this way; Anton (the author) was rather keen on it and I suspect it's painful to change at this point.

[Sascha Silbe (sascha-ubuntu-launchpad)]

It should at least be noted that there's a difference and what exactly uses which unit.

[Sunding Wei (weisunding)]

I hate partman by doing this way. MB should always be 1024KB in computer world, not marketing world. I have this issue with latest Ubuntu 14.04.

[Nehal Mistry (nehalmistry)]

I just encountered this with version 20.04. I created an ESP partition for 259 MB in the installer, but shows as 247 MB in other partition tools (gparted, fdisk, Windows 10). I didn't notice this until a few days after installing Ubuntu. This is the main problem: it's not clear that it deviates from the most common convention.

I understand cjwatson's point that it's not easy to simply change this. But perhaps it's a much smaller change to notify the user somehow? My recommendation would either be to display a message along the lines of "1 MB shown here is equivalent to 1,000,000 bytes". It can be displayed either at the top of the window, or a separate dialog right before in the installer process. I think this would be very useful. If I saw this message I would have partitioned using gparted instead to get the exact layout that I wanted.

[Steve Langasek (vorlon)]

Gparted and fdisk in Ubuntu should never show this as "247MB" and if they do, that is a bug. They may show as 247M or as 247MiB.

Anywhere you enter MB in Ubuntu is to be treated as decimal megabytes, not binary mibibytes". When units are abbreviated to k, M, G for input we should be consistent about using the same unit for output. But it is impossible to have a single set of units that satisfies everyone.

https://wiki.ubuntu.com/UnitsPolicy