How to use iMac as EXTERNAL drive to pull off all data before reformatting

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How to use iMac as EXTERNAL drive to pull off all data before reformatting

What should be my next steps be for salvaging my data off of a sick iMac? I cannot just bring it to an Apple store, because they are closed, due to COVID-19.

My 2013 iMac has problems that I have been unable to resolve with the normal repair procedures: 1) Apple Diagnostics; 2) launch in Safe Mode 3) reinstall Catalina. The iMac continues to be extremely slow, with the spinning color wheel present with every normal system maneuver. Often the iMac re-boots on its own.

The 3TB drive has over 1TB of free space. I have repaired it with Apple Diagnostics, and it reported no major problems. After reinstalling Catalina, the system was still slow, with the spinning color wheel active, even in Safe Mode.

I CANNOT just erase the drive, reformat, and install a clean Catalina, because I have a lot of data that is not backed up, and I need to do that. Time Machine is not working: it will work for a short time, then either slow down or stop completely. After 6 days of trying, I only have 15% of the data backed up. I tried just dragging folders of data to an external drive, but it is just as slow.

Should I:

1) Install Catalina on an external drive and hopefully be able to pull data off from the iMac?

2) Connect my MacBook Pro to the iMac, with the iMac booted in disk mode (can I do that?)

Thanks for any advice!

iMac 27″, macOS 10.15

Posted on May 27, 2020 1:30 PM

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Answer 1

Top-ranking reply

Kappy

Level 10

361,837 points

May 27, 2020 1:35 PM in response to Fastdude

How to use target disk mode to move files between two Mac computers.
You can install macOS on an external drive, then boot the old iMac from the external drive.
You can also remove the HDD from the old iMac, then put it in an external enclosure to keep as either backup or storage.

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Answer 2

Old Toad

Level 10

210,325 points

May 27, 2020 3:31 PM in response to Fastdude

Have you ever run any "cleaning", "optimizing", "speed-up" or anti-virus apps on your Mac?

Download and run Etrecheck. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and use the Add Text button to include the report in your reply. How to use the Add Text Feature When Posting Large Amounts of Text, i.e. an Etrecheck Report

IMPORTANT:

Before running Etrecheck assign Full Disk Access to Etrecheck in the Etrecheck's Privacy preference pane so that it can get additional information from the Console and log files for the report:

Then we can examine the report and see if we can determine what might be causing the slowness problem.

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Answer 3

Old Toad

Level 10

210,325 points

May 29, 2020 2:43 PM in response to Fastdude

So, using my wife’s MacBook Pro (running Catalina), I have the IMac drive attached as an external drive.

Are you referring to Target Disk Mode? Have you tried selecting files or folders, bringing up the Info pane on them, go to the Ownership and Permissions section, unlock it and add yourself or your wife as read and write? Then see if you can copy files to the other EHD.

Or you can connect the two Macs together on a LAN and have you log into your iMac from the MBP as yourself from your wife's MBP? I believe Remote Login and Management would have to be turned on on both in the System/Sharing preference pane.

Then you should be able to copy files to the EHD connected to you wife's MBP.

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Answer 4

TheLittles

Level 10

195,322 points

May 27, 2020 3:20 PM in response to Fastdude

Fastdude Said:

”How to use iMac as EXTERNAL drive to pull off all data before reformatting”

———-

Migrate it All From a Time Machine Backup:

Back up your Mac with Time Machine, then use Migration Assistant to transfer it all in from the backup. Seemingly slow, get an external hard drive with large enough capacity, and place it on a Laptop Cooler.’, while it backs up.

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Answer 5

Fastdude Author

Level 1

103 points

May 31, 2020 4:22 PM in response to Fastdude

WAIT! MORE QUESTIONS!

I have erased both the SSD and HDD volumes of the Fusion Drive. To join them together again I am using the Apple document “How to fix a split Fusion Drive“ (https://support.apple.com/kb/HT201314). I rarely use Terminal mode, so I need advice.

I have rebooted the MBP in Mac OS Recovery (Command-R). Disk Utility shows the MBP volume, plus the now 2 iMac volumes: SSD and HDD

Below are the instructions for Terminal mode. My question is: can I be sure that the Terminal command will ONLY work on the external drives (SSD and HDD), NOT the MBP’s Macintosh HD! Will the Terminal interface ask me which volumes to work on to reset Fusion?

........

“3) Type “diskutil resetFusion” in the Terminal window, then press Return.

4) Type “Yes” (with a capital Y) when prompted, then press Return.

5) When Terminal indicates that the operation was successful, quit Terminal to return to the macOS Utilities window.

6) Choose Reinstall macOS, then follow the onscreen instructions to reinstall the Mac operating system. Your Mac restarts from your Fusion Drive when done.“

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Answer 6

Fastdude Author

Level 1

103 points

May 30, 2020 3:45 PM in response to Fastdude

Major complication today! First, a fuller description of the iMac’s 3TB Fusion Drive. It has been partitioned for 3-4 years into a Mac volume and a smaller BootCamp (Windows) volume.

YESTERDAY I used Target Disk Mode to mount BOTH the Mac and BootCamp volumes on a MBP. I could see the data on the Mac volume.

TODAY wanted to mount them again to unlock various folders, so I could copy the data to another external drive. However, the iMac’s Mac volume did NOT mount. Only the BootCamp volume mounted. I rebooted the iMac while holding down the Option key, which normally allows me to choose which volume I want to use. Now it only shows the “Windows” (BootCamp) volume.

I rebooted the iMac drive in Target Disk Mode on the MBP, to look at it with Disk Utility. I see this picture of the iMac’s HDD Physical Store:

Next I tried to mount this volume (File>Mount). I got this error message:

Next I ran First Aid on this volume, and I got this awful report:

"Running First Aid on “” (disk7s2)

Repairing storage system

Performing fsck_apfs -y -x /dev/disk6s2

Checking the container superblock.

error: object (oid 0x10404): o_cksum (0x2000104010101) is invalid for object

warning: checkpoint 0 fsck_obj_phys failed

error: object (oid 0x900003196): o_cksum (0x400064627032) is invalid for object

warning: checkpoint 1 fsck_obj_phys failed

error: object (oid 0xfffffffffffffffe): o_cksum (0x3ffffffb8fffebff) is invalid for object

warning: checkpoint 2 fsck_obj_phys failed

warning: checkpoint 3 obj->o_type is invalid: (0x40000007)

error: object (oid 0xc80bd8050ecea72d): o_cksum (0xa11fe96d0c4bfc49) is invalid for object

warning: checkpoint 4 fsck_obj_phys failed

error: object (oid 0xaf751d285ac60161): o_cksum (0xbc9d695b14c15fb) is invalid for object

warning: checkpoint 5 fsck_obj_phys failed

error: object (oid 0x70fce): o_subtype invalid, o_subtype 0xb should be 0x0

warning: checkpoint 6 fsck_obj_phys failed

error: object (oid 0x70fdd): o_subtype invalid, o_subtype 0xb should be 0x0

warning: checkpoint 7 fsck_obj_phys failed

error: object (oid 0x471633): o_subtype invalid, o_subtype 0x9 should be 0x0

warning: checkpoint 8 fsck_obj_phys failed

error: object (oid 0x471634): o_subtype invalid, o_subtype 0x9 should be 0x0

warning: checkpoint 9 fsck_obj_phys failed

error: object (oid 0x3e10fffffff): o_cksum (0x3bc7110004000) is invalid for object

warning: checkpoint 10 fsck_obj_phys failed

error: object (oid 0x9e90fffffff): o_cksum (0x55d2b10004000) is invalid for object

warning: checkpoint 11 fsck_obj_phys failed

error: object (oid 0x7ac0901c131b1425): o_cksum (0x15ac380d4409d40) is invalid for object

warning: checkpoint 12 fsck_obj_phys failed

error: object (oid 0xf095cbce3e6ed71): o_cksum (0x26d0f2ee803481e5) is invalid for object

warning: checkpoint 13 fsck_obj_phys failed

error: object (oid 0x90000359d): o_cksum (0x400064627032) is invalid for object

warning: checkpoint 14 fsck_obj_phys failed

error: object (oid 0xcd83bee6bb93389b): o_cksum (0xcb8beb42009e934b) is invalid for object

warning: checkpoint 15 fsck_obj_phys failed

error: object (oid 0xcf01000104010102): o_cksum (0x10036000b562a00) is invalid for object

warning: checkpoint 16 fsck_obj_phys failed

error: object (oid 0x9000036ad): o_cksum (0x400064627032) is invalid for object

warning: checkpoint 289 fsck_obj_phys failed

error: object (oid 0x40404): o_cksum (0x2000104040401) is invalid for object

warning: checkpoint 297 fsck_obj_phys failed

error: object (oid 0xffffffffffffffff): o_cksum (0xfffffffff2cc9c60) is invalid for object

warning: checkpoint 298 fsck_obj_phys failed

error: object (oid 0x70cfa): o_subtype invalid, o_subtype 0x15 should be 0x0

warning: checkpoint 299 fsck_obj_phys failed

warning: checkpoint 302 obj->o_type is invalid: (0x40000007)

error: object (oid 0xffffffffffffffff): o_cksum (0xffffffffffffffff) is invalid for object

warning: checkpoint 303 fsck_obj_phys failed

Checking the fusion superblock.

Checking the EFI jumpstart record.

error: (oid 0x401) nr: invalid o_cksum (0x400064627032)

error: verification/reading of the nx_reaper object failed: Illegal byte sequence

The volume /dev/disk6s2 could not be verified completely.

Storage system check exit code is 8.

Storage system verify or repair failed. : (-69716)

Operation failed…"

I am still hoping I can salvage the data, but I do not know how.

Suggestions? Opinions?

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Answer 7

Fastdude Author

Level 1

103 points

May 29, 2020 2:32 PM in response to Fastdude

Appreciate the suggestions! My most immediate concern is to get my data copied off the iMac drive. After that I will address the iMac slowdown.

So, using my wife’s MacBook Pro (running Catalina), I have the IMac drive attached as an external drive. I also have another empty external drive attached, to which I want to copy the data. The PROBLEM is all of the data folders on the iMac drive are LOCKED, because the MacBook Pro doesn’t have permission to see that data.

What is my next step? If I install Catalina on another external drive and use the same ID and password as on the IMac, will I be able to access and copy off the data?

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Answer 8

Kappy

Level 10

361,837 points

May 30, 2020 7:46 PM in response to Fastdude

That error usually means you have to reformat the drive which will erase everything on the drive. If you were able to access the disk but cannot display any data and got the Diskmanagement dissenter error, then the disk is totally corrupt or has failed. It may be possible to use recovery software to get to the data:

General File Recovery

If you stop using the disk it's possible to recover deleted files that have not been overwritten by using recovery software such as Disk Drill, MAC Data Recovery, Data Rescue II, File Salvage or TechTool Pro. Each of the preceding come on a bootable CD to enable usage without risk of writing more data to the disk. Recovery software usually provides trial versions that enable you to determine if the software would help before actually paying for it. Beyond this or if the drive has completely failed, then you would need to send the drive to a recovery service like Drive Savers, which is very expensive.

The longer the hard drive remains in use and data are written to it, the greater the risk your deleted files will be overwritten. Unfortunately, these programs do not work on SSDs.

Also, visit The XLab FAQs and read the FAQ on Data Recovery.

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Answer 9

Fastdude Author

Level 1

103 points

May 31, 2020 2:10 PM in response to Kappy

The lost data is personal, but losing it is not the end of the world, just a HUGE pain-in-the-a__. I am attempting reformatting, and I hope the hardware (Fusion Drive) is in great shape. I am NOT yet ready to shell out $8000 for an IMac Pro, even though I want one. I also have a new external Thunderbolt SSD drive that will be devoted to Time Capsule backups.

Thanks for all the advice!

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Answer 10

Fastdude Author

Level 1

103 points

May 31, 2020 6:47 PM in response to Fastdude

Additional question: Should I format the SSD and HDD drives in a Late 2013 iMac as APFS, or should I leave them as Mac OS Extended (Journaled)? I have been searching this forum for other questions about resetting a Fusion drive, and I found mention that in older iMacs a Fusion drive cannot be re-made from disks that are APFS.

Also, after formatting the SSD and HDD drives as Mac OS Extended (Journaled), I am thinking I will load Catalina to the HDD, reboot from that drive, and enter Terminal to attempt re-Fusion.

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Answer 11

Kappy

Level 10

361,837 points

May 31, 2020 8:00 PM in response to Fastdude

Here's the man page for the command:

resetFusion

For Fusion Drive machines (two internal disk device hardware

configurations), reset the disk devices in the machine to the

factory-like state of one empty Fusion volume.

This command will only run on a machine that contains exactly

two internal disk devices: one solid-state device (SSD) and

one rotational device (HDD), or, alternatively, two solid-

state devices. This command must be able to make a positive

identification thereof. If these requirements are met, you

are prompted, and if you confirm, the erase and reset begins.

Both internal disk devices are (re)-partitioned with GPT maps,

and then they are turned into (used to create) an APFS Fusion

Drive Container with one APFS Volume.

All internal-disk data is lost. This includes any "extra" par-

titions (e.g. for Boot Camp or other "user" purposes). No

system software is installed and no user data is restored.

After running this command, you should (re)-install macOS on

the machine (on the newly-created APFS Volume); otherwise, the

machine will not be usable (bootable).

You generally must be booted from the Internet Recovery System

(CMD-OPT-R) or from an externally-connected macOS boot disk

(e.g. a USB drive), because you cannot erase a disk that hosts

the currently-running macOS.

Externally-connected disk(s) are not affected. Ownership of

the affected disks is required.

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Answer 12

Fastdude Author

Level 1

103 points

Jun 1, 2020 10:52 PM in response to Kappy

SLOW AS MOLASSES! Hardware problem?

So I successfully restored my 3TB Fusion Drive and installed Catalina. WiFi is hooked up, and it is fast, according to Google Speedtest: Over 400 Mbps upload; over 500 Mbps download. I linked my iCloud, but that is all I have done. There is NO third party software installed.

The problem is ALL functions CRAWWWL. Here are some timed examples:

Boot from Power off: 1:56

From Entering Password to full Desktop on screen: 4:58

Launch Safari: 1:15

In Safari, bring up the Google Speedtest web page: 0:52

Quit Mail: 1:26

Launch Calendar: 0:34

Obviously I think there is still something wrong with this Late-2013 iMac, but I am going play with it for a few days and see if it improves, worsens, or stays the same. If the speed does not improve. then I have to have it seen somewhere.

Suggestions?

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Answer 13

Fastdude Author

Level 1

103 points

Jun 5, 2020 3:35 PM in response to Fastdude

Thought I would wrap this thread up. On Monday I spent 90 minutes on the phone and online with Latanya, an Apple CS rep, and it was worth it! We went through my whole story, and I gave Latanya access to my desktop, which she could watch while I did the various maneuvers that she wanted to see. She watched my slow system, then had me pull up every Apple info window that exists for Catalina. Everything looked fine! No apparent problems with the OS, RAM chips, SSD and HDD drives. RAM usage was entirely normal for the loaded apps, with most RAM not being used. No lurking 3rd party software. We looked at activity logs I did not know existed. Finally Latanya went to her Senior Manager. He could only say that it HAD to be a problem with one or more of the RAM chips, even though they looked OK.

They had two final maneuver for me. If they did not improve things, then I would have to bring it somewhere for service, which means I would spend money. I was to 1) reinstall Catalina from Internet-based Recover Mode, and 2) pull the RAM chips and leave one 8GB chip in place. I the speed increased to normal, then swap the other chips in to see which one caused a slowdown.

I never had to use step 2)! This was my second internet-based install, but this time It worked. My iMac is back to normal. I don’t know why the OS got corrupted, but it did. I lost data, but not everything.

Oh, and Time Machine is backing up everything, as we speak.

Thanks to all for your suggestions!

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