Add backup disk usage monitoring and deleting old backups

[Alloc]

Options could be:

• Only allow XX MiB of disk space for backup folder, if exceeding delete old backups
• Always only keep the N newest backups

Anything else?

[Alloc]

Options:

• Only N newest backups
• Only X MiB of backup storage
• Only limited backup age (e.g. only backups for last 24h)
• Minimum number of backups to keep at any time

• Compress old backups

Change cronjob to run at lower priority (nice -n 15)

[alloc]

In 52:

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