What Is MDS?

If you own a Mac, you have probably pulled up the Activity Monitor now and again whenever your Mac slows down and starts to lag.

You have noticed something that comes up under the process name of ‘MDS’.

This is the one with the usual high CPU utilization percentage – but what does it mean and does that high CPU utilization percentage mean it is causing your computer to crash?

Find out here everything you need to know about MDS including what is and what its purpose is on your Mac OS.

This way you can understand everything in your Activity Monitor better so you can get to the root cause of any issues you face in the future.

What Is MDS

What Is MDS?

MDS actually stands for ‘metadata server’ and its process is a part of Spotlight, a powerful search feature built-in in your Mac OS X.

So, in actuality, MDS is harmful and is not the thing behind your Mac becoming sluggish or slow – it’s just part of the Spotlight search tool that helps manage the index used to give you quick search results.

MDS is also closely related to another process found in the Activity Monitor called ‘mdworker’.

Mdworker stands for metadata server worker, which does the hard work of indexing your files. This helps make using the searing tool Spotlight be as quick as possible.

So basically, MDS and mdworker are both a part of Spotlight, a search tool that is built into your Mac.

Why Does MDS Use So Much CPU?

It’s actually quite normal for MDS and mdworker to use a lot of CPU.

If you have recently migrated all of your files and apps from another Mac device or just added a whole new bunch of files to your Mac, then your MDS and mdworker will take up a huge amount of power and memory.

This is because the processes are needed to work to build an index of all these new files so it can continue to power a quick and fast search tool.

To check that the MDS and mdworker are hard at work indexing your files, open up Spotlight and you should see an indexing notification next to the progress bar – a sure sign that the processes are up and running!

This means that Spotlight is creating your index and why the CPU utilization percentage is so high for MDS and mdworker.

This process can take a few hours to complete, depending on other factors like your processor speed and hard drive.

However, Spotlight is not programmed to use up all of your processing resources while you are active on your Mac.

It takes a backseat until your Mac is left idle and not on battery power so it knows that you don’t have anything more important that takes up processing resources.

This means that when you are doing something on your Mac that requires a lot of processing, Spotlight will back off and your MDS and mdworker processes will not take up as much CPU utilization percentage.

Once your Mac is idle, Spotlight will use up as many resources as it needs to try and get these processes complete more quickly.

This explains why sometimes in Activity Monitor, the CPU utilization percentage of MDS and mdworker can vary between as low as 30% and as high as 90% at different times – it’s because Spotlight purposely slows down when your Mac’s processing intensity is high and then picks up the slack when your Mac is idle.

When the processing is done, these names should vanish from your Activity Monitor.

My Spotlight Processes Won’t Stop

If you find that MDS and mdworker processes are constantly appearing in your Activity Monitor and never seem to finish doing their job, this means that they are constantly using your CPU and taking up memory even days after the indexing should have been completed.

This is a sign that your index has been corrupted and you need to fix this by rebuilding your Spotlight index.

One way you can do this is by adding your hard drive to the Excluded Locations list and then remove it again. Another way is to open up Terminal and run this command:

Sudo mdutil -E /

Nevertheless, your Spotlight index will need to be rebuilt but once the process is done, the MDS and mdworker process will stop taking up CPS utilization.

Rebuilding Your Spotlight Index

Rebuilding Your Spotlight Index

To start rebuilding your Spotlight Index, head-on into system preferences and click on Spotlight itself.

Then, click on the privacy tab – this is where you can add files to prevent Spotlight from searching them and taking up your CPU.

Click and drag your entire hard drive onto the privacy window. On the other hand, you can reindex a folder or specific file instead but sometimes it’s easier to just reindex your entire main system drive.

A prompt will pop up asking you if you really want to prevent Spotlight from searching your Mac – just click okay and then the hard drive will appear in the bottom box.

Now, you need to remove it.

Click on the minus button at the bottom of the screen and thi will cause Spotlight to reindex your drive.

Now, you should receive accurate search results and the MDS and mdworker process will fix itself and vanish from your Activity Monitor.

If this doesn’t work, open a terminal window by going to Applications and heading into the utilities folder. In the box, type in the command:

Sudo mdutil -E /

You will then be asked to type in your password, then hit enter and Spotlight should reindex itself.


So what is MDS?

MDS stands for metadata server and it is a process that is a part of Spotlight, a search tool embedded in Macs. It’s a harmless process that will often crop up in your Activity Monitor now and again.

It takes up a varying amount of CPU depending on if you recently moved a lot of files onto your Mac, but sometimes the processes won’t stop for days and glitch to constantly take up a lot of your processing time and memory.

When this happens, just rebuild your Spotlight index by following the above steps.

We hope this guide has helped you understand certain parts of your Activity Monitor better so you can understand what’s going on with your PC when it starts to slow down.

Albert Niall
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