# The always-on Mac: a $600 computer that works while you sleep

**What it does:** turns one cheap, permanently awake Mac into the machine that runs your long
jobs, your schedules and your backups, so your laptop lid can close and nothing dies with it.
Hang USB drives off it and it also becomes the cheapest large-file storage you will ever build,
for reasons that are a quirk of how backup pricing works.

**What it saved:** every overnight job that used to be a laptop left open on a desk. It also
replaced a four-figure-a-year cloud storage bill with a $99-a-year one, which is the part most
people do not know is possible.

**Shown at:** AI Open House, by Colton Mulligan.

## What you need

| Tool | Cost |
|------|------|
| A Mac mini (a used base model is plenty) | about $400 to $600 used |
| Your usual AI agent CLI, signed in on that machine | your existing plan |
| USB hard drives, as many as you like | about $15 to $20 per TB |
| Backblaze Personal Backup, one license | about $99 a year |
| A battery backup under the desk | about $130, see the UPS recipe in this library |

## Set it up so it never needs you

Four settings do almost all of the work:

1. **Never sleep, ever.** System Settings, Energy: prevent automatic sleeping with the display
   off, and turn on "Start up automatically after a power failure." An unattended machine that
   sleeps is an unattended machine that silently stops working.
2. **Auto-login.** After a power cut, the machine has to come all the way back to a logged-in
   desktop by itself, or every scheduled job waits for you to walk over and type a password.
3. **Schedules, not habits.** Use the operating system's own scheduler (`launchd` on a Mac) for
   anything recurring. Give every job a log file and read it once.
4. **One job, one machine.** Pick which machine owns each job and disable the copy everywhere
   else. Two machines running the same sync is how you get two half-finished results.

Then let it do the work: long builds, nightly media processing, scheduled research, backup
verification, the jobs you would never leave a laptop open for.

## The storage loophole worth knowing

This is the part that surprises people, and it is not a trick, it is just how the product is
priced.

- **Unlimited personal backup covers local volumes.** One Backblaze Personal Backup license, at
  about $99 a year, backs up that computer **and every USB drive attached to it**, with no cap
  on how much. Ten drives on one machine is still $99 a year.
- **It will never back up a NAS.** Network drives, network shares and NAS devices are excluded
  from Personal Backup as company policy, not as a setting. There is no configuration that
  changes it, and their own sanctioned path for a NAS is their paid object storage.
- **So the math inverts.** For a large media library, object storage runs roughly $7 per TB per
  month, which is well over a thousand dollars a year and grows forever. USB drives on the
  always-on machine, under the license you already pay for, add $0 a year. For us the gap was
  about thirteen to one.
- **What that makes possible:** park anything large where it is both local and backed up. Video
  masters, raw footage, build artifacts, the assets behind an App Store submission, anything you
  need to be able to retrieve later and do not want eating your laptop's disk.

## Three traps that will cost you terabytes

Learned the hard way. All three come from the same fact: this kind of backup tracks files **by
their path**, so anything that changes a path looks like a brand new file.

1. **Never rename a backed-up drive.** Renaming the volume presents every file on it as new and
   re-uploads the whole thing. Terabytes, over your home connection, for nothing.
2. **Never re-nest the contents.** Pushing a drive's files one folder deeper is the same mistake
   wearing a hat. If the files sit at the drive root, keep them at the drive root.
3. **Wiping a drive is worse than renaming it, because it is silent.** A reformatted drive can
   drop out of the backup set entirely, and nothing tells you. We wiped a drive, renamed it,
   seeded it with 9.5 TB of irreplaceable family footage, and the backup reported "complete"
   that night with nothing queued. It had simply never adopted the drive.

**So verify adoption after any reformat, rename or new drive.** On a Mac, a drive that is really
being backed up has both a `.bzvol` folder at its root and an entry for its mount point in
`/Library/Backblaze.bzpkg/bzdata/bzinfo.xml`. Check for both. "The last backup said complete" is
not evidence: a drive it does not know about generates no work and no warning. Re-adopting a
drive takes one visit to the Backblaze settings pane to tick the box.

## The prompt

```text
I have an always-on Mac and some USB drives attached to it, and one Backblaze Personal Backup
license. Verify my backup is real, not just reporting success.

For every attached volume, tell me:
- whether a .bzvol folder exists at its root
- whether its mount point appears in /Library/Backblaze.bzpkg/bzdata/bzinfo.xml
- how much data it holds, and how much Backblaze thinks it has uploaded

Then list any volume that holds data but is NOT in the backup set, loudly and first, and tell me
exactly what to click to add it. Do not treat "last backup completed" as evidence that a
particular drive is covered.

Then write that whole check as a script I can run on a schedule, and have it alert me only when
a volume with data is missing from the backup set.
```

## Stack card

```text
WHAT IT DOES:     One cheap always-on Mac runs the long jobs and makes USB drives into backed-up storage
AI / MODEL:       Any agent CLI, running on that machine
STACK:            Mac mini, launchd schedules, USB drives, Backblaze Personal Backup, a UPS
COST TO RUN:      About $99 a year for unlimited local-volume backup, plus the hardware once
TIME SAVED:       Every overnight job, plus roughly thirteen times the cost of cloud object storage
TIER SHARED:      runbook plus the verification prompt
```

Prices and product policies move. Check the vendor's own page before you build on this.

Built by Colton: https://builtbycolton.com

From the AI Open House free library: https://aiopenhouse.co/guests/#library