How can a file created by dd be bigger than the partition?

What your teacher is most likely referring to is something called "sparse files". These are files which grow as they are written to, with the underlying disk holding the magic - thus, provided that the filesystem is empty (and specifically writing 0's is not empty) its possible to create a 10 gig sparse file/block device using only a fraction of that on disk.

Look at this superuser link for more details on sparse files - especially the first response which explains how to do it in DD.

davidgo

Posted 2018-03-11T22:16:24.047

Reputation: 49 152

oh okay that's what i was thinking it's like a having "1000 m² of void in 10m²" in some way ? – Henley n – 2018-03-11T22:49:30.060

2The filesystem doesn't record the zeroes, but rather records the seek() (which can skip forward or backward in a file)... It's sort of like holding an IOU for n apples, rather than a bucket of n apples. – Attie – 2018-03-11T22:52:49.147

2Its a bit similar to those fake USB disks you get out of China which claim to be 128GIG, but are actually 4 gig - they just tell the OS they have more space then they do - but when you run out of actual space, bad things happen. (Of-course, sparse files are designed to grow as needed, so you don't have problems until its more then the underlying disk, and they probably won't silently drop all your data) – davidgo – 2018-03-11T22:55:53.637

lmao fanks for the explaination – Henley n – 2018-03-11T23:55:26.240

How can a file created by dd be bigger than the partition?

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