How to create limited-size directory

What an issue I've got

Today I've got a task to test (and fix) how the application behaves during a backup when it does not have a space on the device.
As result, there shouldn't be any new files once the backup is failed with "no space left" error.

How did I investigate the issue

So far, I see the following options for how to reproduce the issue:

• to have enormous application data to backup, either on some shared machine or generate the content locally
• to create a limited-size directory and try to write a backup there

First option is time-consuming to reproduce it locally, so let's start with creating limited-size directories.

I have two target environments for testing: Windows 10 and Debian-based Linux.
I've chosen Ubuntu 18.04 because I have the VM already installed.

So, let's make a backup for the newly installed application and check its size.
And empty backup is 8.5Mb. It is suspicious the app has an 8Mb backup from scratch, and I will write it down to fix later, but I have another issue so far.

Windows

I haven't found a way to create a limited-size directory on Windows, but I can create a limited-size virtual disk and use it for my purposes.

1. Go to Disk management
2. Select your local disk and choose "Create VHD" in "Action"
3. Choose Virtual Disk file location and set disk size. For my pupose I need 10Mb (8Mb for backup plus some extra for partitions and system information) and I need "Fixed size".
4. Initialize the new disk (choose Master Boot Record)
5. Create new simple volume.
6. Next... Next... Next... and disk is ready

Wow!!! It took almost 7Mb from the original 10Mb for system data. WOW!!!

But... it is enough for my purposes.

Linux

1. Create file with size you need

➜  touch 10mbarea
➜  truncate -s 10M 10mbarea

1. Create file system with the file

➜  mke2fs -t ext4 -F 10mbarea
mke2fs 1.46.5 (30-Dec-2021)
Discarding device blocks: done                            
Creating filesystem with 10240 1k blocks and 2560 inodes
Filesystem UUID: 03249ba7-6abc-4afb-a496-b5857f529859
Superblock backups stored on blocks: 
        8193

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (1024 blocks): done
Writing superblocks and filesystem accounting information: done

1. Create a directory you will use later

➜  mkdir 10mbup

1. Mount the file system to the folder

➜  sudo mount 10mbarea 10mbup 
[sudo] password for vbochenin: 

1. And limited size directory is ready

➜  df -h 10mbup              
Filesystem      Size  Used Avail Use% Mounted on
/dev/loop1      8.3M   14K  7.5M   1% /home/vbochenin/10mbup

Once limited size directories created, I may specify them as backup target directory and run the same empty backup.

If you find the post helpful, please support me and: