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 a result, there shouldn’t be any new files when the backup fails with a “no space left” error.

How did I investigate the issue

So far, I see the following options for reproducing the problem:

to have huge application data to back up, either on a shared machine or generate the content locally
to create a directory of limited size and try to write a backup to it.

The first is time-consuming to reproduce locally, so let’s start by 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 already have the VM installed.

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

Windows

I have yet to find a way to create a limited-size directory in Windows. However, I can make a limited-size virtual hard disk and use it.

Go to Disk management
Select your local disk and choose “Create VHD” in “Action”.
Choose Virtual Disk file location and set disk size. For my purpose, I need 10Mb (8Mb for backup plus some extra for partitions and system information), and I need “Fixed size.”
Initialize the new disk (choose Master Boot Record)
Create new simple volume.
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

Create file with size you need

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

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

Create a disrectory you will use later

    ➜  ~ mkdir 10mbup

Mount the file system to the folder

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

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 the limited-size directories are created, I can specify them as the backup target directory and run the same empty backup.

What an issue I’ve got

How did I investigate the issue

Windows

Linux

About Vladislav Bochenin