Bypass Backblaze's Locked System Drive to Pause C:\ Scans Temporarily

Backblaze's dialog refuses to clear the checkbox for your system drive on a normal click, but the lock has a simple bypass: hold down Ctrl, then click the checkbox next to C:\ under Settings → Select Hard Drives to Backup. The drive is deselected without the refusal message, Backblaze stops walking C:\ for files, and your other selected drives keep backing up as usual.

Why the system drive is locked in the first place

Personal Backup treats the drive Windows is installed on as mandatory. The design assumption is that the most irreplaceable data — user profiles, the Desktop, Documents, browser bookmarks, application settings — lives on C:\, so the client refuses with the message "Backblaze does not allow you to unselect your main hard drive." It is a guardrail aimed at preventing less experienced users from accidentally emptying their backup selection, not a technical limitation of the backup engine itself. Because it is enforced only in the interface, the selection behind it can still be changed — which is exactly what the modifier-key trick exploits.

Deselecting C:\ step by step

1. Right-click the Backblaze icon in the system tray and open Settings....
2. Switch to the Select Hard Drives to Backup page.
3. Hold Ctrl and click the checkbox beside C:\.
4. The checkbox clears and the "main hard drive" refusal does not appear. Leave every other drive checked.
5. Confirm with OK to apply the new selection.

If the drive stubbornly stays checked, the click probably landed before the key was fully held: reopen the dialog and try again, keeping Ctrl pressed until the click registers. Once applied, any scan of C:\ that was in progress is dropped along with the drive's entry in the selection.

What changes once C:\ is deselected

• Scan activity on the system drive stops. The heavy read traffic that motivated the change disappears, while the client continues scanning and uploading your other drives.
• Files created or edited on C:\ during the pause are not backed up. Keep the pause only as long as your I/O problem requires, and avoid installing or editing anything critical in that window.
• Existing uploads survive for a limited time. Backblaze keeps data from a deselected drive on its servers for roughly 30 days before purging it, so treat that as the maximum sensible length of your pause.

Alternatives if you would rather keep C:\ protected

Unchecking the system drive leaves a gap in your backup, so if that is uncomfortable, reduce the load instead of pausing it:

• Confine Backblaze to a backup window. Under Settings → Schedule, switch from Continuously to Once Per Day at a quiet hour, so scanning and transfers happen overnight instead of while you work.
• Wait out a rescan. Intense reads typically follow an installation, a reboot, or a large batch of changed files. Once the client catches up, its routine passes over an idle system drive are short.
• Exclude churn-heavy folders. Caches and temp directories inflate upload volume, though exclusions do not eliminate scanning entirely — the client still walks the volume's directory tree to build its file list.
• Drop the process priority. Setting bztransmit.exe and bzbui.exe to a lower priority in Task Manager softens the impact at best; it will not stop the reads.

Re-enabling C:\ when the pause is over

Return to the same dialog and click the checkbox for C:\ again — hold Ctrl once more if a plain click is ignored. Backblaze then performs a fresh scan of the volume: files still present on the servers are reconciled without being uploaded again, while anything that changed during the pause, or was already purged after the 30-day window, is uploaded as new. Let that scan finish before concluding the workaround did not take.

Frequently Asked Questions

Is the Ctrl+Click bypass an official feature?

It is undocumented behavior built into the client rather than a published option. It changes only your local backup selection, exactly as toggling any other drive would, but do not expect it in the manual or an endorsement from support.

Will my already-backed-up C:\ files disappear immediately?

No. Content from a deselected drive is retained on Backblaze's servers for about 30 days. Re-select the drive within that period and the data is still there; afterwards, purged files must be uploaded again from scratch.

Can I avoid the reads by excluding folders instead?

Only partially. Exclusions cut what gets uploaded, but the scanner still walks each selected volume to enumerate files, so the read activity on C:\ continues.

Does pausing C:\ affect the other drive's backup?

No. Selection is per drive. Any drive that remains checked keeps scanning and uploading on the normal schedule throughout the pause.

Why does Backblaze read C:\ so much when I changed almost nothing?

The client rescans selected volumes when it starts and then periodically, comparing its internal index against what is on disk. Even an apparently idle system drive produces noticeable reads during those passes, especially right after installation or a reboot.