mdsync high CPU usage on Mac

What is mdsync on Mac?

Spotlight search feels simple on the surface: you type, results appear. Underneath, macOS runs an entire stack of metadata services to keep that experience fast and accurate. mdsync is one of those services.

It belongs to the same family as mds, mds_stores, and various mdworker processes that build and maintain Spotlight’s search index. Its role is to synchronize and update metadata across volumes so Spotlight results remain in step with what’s actually stored on your disks.

On current macOS versions, this covers more than just the internal drive. mdsync often becomes active when you:

• plug in external USB or Thunderbolt disks,
• connect APFS Time Machine destinations, or
• work with large, constantly changing data sets.

During the first indexing pass or after major changes, it’s normal to see mdsync briefly float to the top of Activity Monitor’s CPU list.

The important point is that mdsync is a built-in, Apple-signed component. It isn’t malware, and it isn’t a random third-party service. Most of the time, it does its work quietly in the background. The problem starts when indexing gets stuck, or when the workload is so heavy that mdsync monopolizes CPU cycles for long stretches.

Why mdsync can spike CPU usage on Mac

Under normal conditions, mdsync wakes up to do a job, processes a batch of metadata, and then steps aside. CPU spikes are expected while this work is in progress. They become a problem when the spikes are intense and never really subside.

Typical triggers include:

• Fresh or rebuilt Spotlight index
  After a macOS upgrade, a clean install, or a full Spotlight reset, the system must re-index everything. On machines with large volumes, mdsync and its sibling processes can sit at high CPU usage for quite a while until the job is done.
  
• Huge external or Time Machine drives
  Multi-terabyte SSDs, media archives, and Time Machine destinations are classic sources of sustained activity. Spotlight may try to index not only the live data but also a history of snapshots, which can keep mdsync busy for hours.
  
• Constantly changing data
  Developer projects, virtual machine images, large photo or video libraries, and cloud sync folders generate constant writes. Spotlight tries to keep its view of this data current, and mdsync gets pulled in to keep the metadata aligned with reality.
  
• Corrupted or problematic Spotlight index
  If a Spotlight index is corrupted, or if a particular file confuses a metadata importer, Spotlight may keep retrying. The result looks like a loop: mdsync repeatedly works on the same data set without making progress, and CPU usage remains high.
  
• Third-party software interference
  Backup tools, antivirus utilities, sync clients, and “cleanup” apps that continuously touch large numbers of files can amplify Spotlight’s workload. Two or three such tools stacked together can easily push mdsync and related processes into overdrive.
  
• Side effects of malware or PUAs
  This is the least common scenario, but it shouldn’t be dismissed. Some Mac threats generate abnormal file system activity, drop files repeatedly, or mimic system process names. In these cases, mdsync’s high CPU usage may be a symptom of the wider problem rather than the root cause.
  

Short-lived spikes when something obvious is happening – such as a big OS update or the first connection of a new drive – are normal. The red flag is sustained high CPU usage that goes on for hours or days with no clear explanation.

First fixes on the checklist

Before you resort to heavier measures, it’s worth running through a quick set of checks. These often resolve or at least narrow down the issue.

1. Confirm that mdsync is really the culprit

• Open Finder.
• Choose Go > Utilities.
• Open Activity Monitor.
• Click the CPU tab and sort by % CPU.
• Look for mdsync, mds, mds_stores, or mdworker near the top.

2. If mdsync spikes briefly and then drops back down, that’s typical indexing. If it stays glued to the top of the list, move on.
3. Ask whether indexing is expected right now
   Consider what changed recently:
   

• Did you upgrade or reinstall macOS?
• Did you create a new user account?
• Did you attach a new or very large external drive?

4. If the answer is yes, you may simply need to let Spotlight finish its work:

• Plug your Mac into power.
• Keep the lid open and let it stay awake for a while.
• Watch Activity Monitor periodically to confirm that CPU usage is trending down over time.

5. Restart the Mac
   A reboot clears stuck Spotlight jobs and closes apps that may be triggering repeated indexing.
   

• Open the Apple menu and select Restart…
• After the restart, open Activity Monitor again and see whether mdsync behaves better.

6. Disconnect non-essential external drives
   If several USB or Thunderbolt volumes are attached, one of them may be generating a disproportionate indexing workload.
   

• In Finder, click the Eject icon next to each external volume you don’t immediately need.
• Once the drive disappears from the sidebar, unplug it.

7. If mdsync calms down after a particular drive is removed, you’ve found a prime suspect.
8. Test in Safe Mode
   Safe Mode loads only essential system extensions and can help reveal third-party interference.
   

• On Apple silicon Macs:
  • Shut the Mac down.
    • Press and hold the power button until startup options appear.
    • Select your startup disk, hold Shift, and click Continue in Safe Mode.
• On Intel-based Macs:
  • Restart and immediately hold Shift.
    • Release the key when you see the login window with Safe Boot in red.

9. Log in, let the system sit idle for a bit, and check Activity Monitor. If mdsync looks normal in Safe Mode, a third-party component is probably contributing to the problem.

How to fix mdsync high CPU usage on Mac (manual steps)

The steps below aim to cut unnecessary work mdsync is doing, identify possible conflicts, and rule out impostor or auxiliary processes that keep Spotlight busy. Follow them in order and check CPU behaviour after each cluster of changes.

Step 1: Force-quit mdsync once via Activity Monitor

This doesn’t remove the process – macOS will relaunch it if needed. But it can break a stuck loop.

• Open Activity Monitor via Finder > Go > Utilities.
• Click the CPU tab.
• Select mdsync in the list.
• Click the Stop (⛔) icon in the upper-left corner of the Activity Monitor window.
• In the dialog that appears, click Force Quit.

If mdsync immediately jumps back to the top of the CPU list and stays there, treat that as a sign that something deeper – such as a damaged Spotlight index or a noisy volume – is still in play.

Step 2: Rebuild the Spotlight index for the startup disk

If indexing runs feel endless, forcing Spotlight to throw away the old index and build a fresh one is the next logical step.

• Open System Settings from the Apple menu.
• Go to Siri & Spotlight (or Spotlight, depending on your macOS version).
• Click Spotlight Privacy (or the similarly named button).
• Click the + button and add your startup disk (for example, Macintosh HD).
• Confirm that you want to prevent Spotlight from searching this disk.
• Wait about a minute.
• Select the same disk in the list and click the – button to remove it from Spotlight Privacy.

Spotlight will now rebuild the index from scratch. Expect mdsync and related processes to spike again for a while, but CPU usage should eventually taper off instead of remaining permanently high.

Step 3: Exclude heavyweight or rarely searched locations

You don’t need Spotlight to index every volume and archive you own. Excluding bulky or noisy locations can dramatically reduce how hard mdsync has to work.

• Stay in the Spotlight Privacy section of System Settings.
• Click the + button.
• Add locations such as Time Machine backup destinations, large external media libraries, virtual machine folders, and folders used by backup or sync tools.
• Repeat until all non-essential locations are added.
• Close System Settings.

From this point on, Spotlight (and therefore mdsync) ignores those paths, which can noticeably lower indexing load.

Step 4: Review Time Machine and other backup tools

Time Machine and third-party backup apps generate a lot of file system activity. When their data is indexed, metadata services get busy too.

• Open System Settings and select Time Machine.
• Review the list of backup disks and remove any you no longer use regularly.
• If you use additional backup apps, open their settings and check where they store data and how often they run.
• Where possible, connect backup disks only when you intend to run backups instead of leaving them attached all the time.

After these adjustments, let the Mac run through a couple of backup cycles and then check Activity Monitor again to see whether mdsync’s CPU usage is more moderate.

Step 5: Run First Aid on volumes that seem “noisy”

If a particular internal or external disk consistently coincides with high mdsync usage, it may have file system issues that confuse Spotlight.

• Open Disk Utility from Applications > Utilities.
• In the sidebar, select your startup disk under Internal.
• Click First Aid in the toolbar.
• Confirm that you want to run First Aid and wait for the check and repair to complete.
• Repeat the same procedure for any external disk that appears to trigger mdsync spikes.
• When all checks are done, restart your Mac.

A clean file system gives Spotlight a more predictable structure to index and can prevent repeated retries that keep mdsync busy.

Step 6: Temporarily pause Spotlight indexing via Terminal (advanced)

If you need immediate relief – for example, to finish work while on battery – you can pause indexing system-wide. This will make Spotlight search incomplete while it’s disabled.

• Open Terminal from Applications > Utilities.
• Type the following command:
  sudo mdutil -a -i off
  
• Press Return.
• Enter your administrator password when prompted and press Return again.

This stops indexing for all mounted volumes and should quickly pull mdsync’s CPU usage down. When you are ready to turn indexing back on, run:

sudo mdutil -a -i on

After re-enabling indexing, it’s a good idea to keep the Mac on power and idle for a while so Spotlight can catch up in a controlled way.

Step 7: Reset Spotlight’s index from the command line (advanced)

If the graphical rebuild doesn’t help, a full reset via Terminal can address deeper Spotlight index corruption.

• Open Terminal again.

Run the following command to erase and rebuild the index for the startup volume:

sudo mdutil -E /

• If other volumes appear problematic, repeat the command and substitute their mount points (for example, /Volumes/ExternalDisk).
• Restart your Mac once the commands complete.
• Leave the Mac plugged in and awake so it can re-index without interruption.

This more drastic reset often leaves Spotlight and mdsync in a healthier state, at the cost of a one-time indexing session that may take some time on large disks.

Check for a malware or PUA facet of the mdsync issue

Most mdsync CPU spikes are mundane side effects of indexing. Still, if high CPU usage coincides with other warning signs, the picture changes. Take a closer look if you notice:

• persistent browser redirects or unwanted search engines;
• aggressive pop-up ads claiming your system is infected;
• unknown configuration profiles in System Settings;
• strange login items or launch agents you don’t remember installing.

Adware and potentially unwanted apps tend to generate constant file system and network activity, create and delete files repeatedly, and tamper with browser settings. All of that adds background noise which Spotlight has to track, keeping mdsync busier than it should be.

Some threats also imitate system process names to blend in. While mdsync itself is legitimate, you want to be sure there are no additional components on the system misusing resources or attempting to piggyback on its activity. Running a reputable security tool to scan for adware, PUAs, and other threats is a reasonable step at this stage.

How to prevent mdsync CPU spikes on Mac going forward

Once you’ve stabilized mdsync and Spotlight, a few practices will help keep things that way:

• Keep macOS updated
  System updates regularly include quiet fixes for Spotlight and metadata-related bugs. Installing them promptly is an easy way to benefit from those improvements.
  
• Be selective about what Spotlight indexes
  Avoid indexing bulky archives, rarely used external volumes, or folders that change constantly but never need to show up in search. Use the Spotlight privacy list to keep the index focused on what you actually search.
  
• Avoid stacking too many background utilities
  Running several antivirus tools, backup apps, and “cleaners” simultaneously can create overlapping workloads. Use fewer, better-chosen tools instead of throwing everything at the system at once.
  
• Manage backup disks wisely
  Let Time Machine do its job, but connect backup disks for specific backup windows instead of leaving them attached 24/7, especially if they hold years of snapshots.
  
• Investigate sustained fan noise
  If your Mac is hot and loud for no obvious reason, open Activity Monitor and find out what’s responsible. It’s easier to fix a resource hog early than after hours of thermal stress.
  

Wrapping it up

mdsync is an integral part of how Spotlight and other macOS components keep track of your files. Occasional CPU spikes are the cost of maintaining a fast, system-wide search index, particularly after major changes or when large volumes are involved.

These spikes only become a real issue when they turn into a constant state of high CPU usage that slows your Mac to a crawl. By confirming what mdsync is doing, rebuilding and tuning the Spotlight index, checking external and Time Machine drives, and ruling out malware with a reputable security tool, you can almost always return this process to its usual, unobtrusive behavior.

The key is to distinguish between healthy background indexing and a loop that is clearly stuck. Once you make that distinction, keeping both mdsync and your Mac’s performance under control becomes a matter of methodical, manageable steps.

FAQ

1. Does mdsync mean my Mac is infected with a virus?

2. How long should mdsync high CPU usage last?

3. Is it safe to force-quit mdsync in Activity Monitor?

4. Can I disable mdsync permanently?

5. Why does mdsync spike CPU whenever I plug in a specific drive?