First Aid External Hard Drive Mac

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First Aid External Hard Drive Mac

Mac OS Diagnostics The MacOS has great tools for testing hard drives. This program is called First Aid. Always backup your data before running First Aid scans of your hard drive. If there is a bad sector, any data that may have been accessible before running “Repair Disk” will likely become inaccessible once the bad sector is re-allocated. Firstly, connect your external drive to your Mac using a working cable. As soon as it gets detected it, Time Machine will automatically display the following prompt. Just select the 'Use as Backup Disk' feature to proceed. In case you don't get this prompt, then you can manually launch the Time Machine tool from Mac's System Preferences. Repair Seagate External Hard Drive in First Aid Hard Drive Drivers Windows 10. Applies to: Mount Seagate external disk to make it work on Mac. If the Seagate drive is unmountable or the Mount icon is greyed out, it could be some disk errors that prevent your Mac from recognizing/detecting the drive correctly. Click First Aid then hit Run to verify and repair logical issues with the hard drive. Check the SMART status of the external hard drive if it unmounts intermittently. Open Disk Utility then check the SMART Status of the external hard drive. I recently plugged the external drive into my Mac, it spent a long time running fsckhfs and finally showed this dialog: Running disk utility gives a lot of Invalid extent entry messages along with the conclusion First Aid process has failed. My intuition would be to copy the whole disk to a new drive.

External is a Seagate 2TB Backup Plus Desktop Drive for Mac. I'm running 10.11.6 on a Mac Mini. It's connected by FW800. Disk Utility First Aid for just that volume stalls after the 'Invalid Extent Entry' note.

I ran Disk Utility on the entire external drive (all volumes). Result: [All checks seem good, then...] 'Problems were found with the partition map which might prevent booting. Operation successful.'

Other 3 volumes on that Seagate seem to work fine. One of those volumes has secondary Time Machine backups.

After restart, Mac without prompting says: 'OS X can’t repair the disk “Backup.” You can still open or copy files on the disk, but you can’t save changes to files on the disk. Back up the disk and reformat it as soon as you can.'

I assume I should erase that Backup volume but my concern is I'm afraid erasing that Backup volume might screw with the other volumes, and my only other TM backup, which is on another volume of the same external HD.


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The invalid extent entry error basically means the directory on your drive is corrupted. In other words the index of what files are stored and where they're stored is all mucked up.

This can be repaired but not without risk. You basically have two options if you still want to keep using this drive:

  1. Use a third party disk utility that can repair the corrupted directory (e.g. DiskWarrior, Techtool Pro, etc)
  2. Reformat the partition

Note: I have no affiliation whatsoever with either DiskWarrior or Techtool Pro.

Regardless of the option you choose I would still recommend manually backing up any files you can still access to another drive. Obviously this is a must do if you opt for the second option.

As to your concern about accidentally reformatting the other partitions, this shouldn't be a problem as long as you're only selecting the particular partition (or volume) with the error.

More specifically:

  • launch Disk Utility
  • select the partition in the sidebar
  • click the erase tab
  • make sure the format in the drop-down menu is the one you want
  • give it a name
  • click on Erase

Seagate External Hard Drive Mac

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