iMac Cannot Restore 'Macintosh HD' to External HDD (File Too Large - Error 27)

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iMac Cannot Restore 'Macintosh HD' to External HDD (File Too Large - Error 27)

Hi All,

Apologies in advance for the long post, but I'm in quite a predicament that's been wrecking my brain for the past 24 hours and need some help as I could potentially lose very important data.

Quick Rundown: My iMac will simply not boot from the built-in 'Macintosh HD' - I power it on, hear the chime and see the black screen with Apple Logo and Loading Bar. The Bar reaches 100% and just hangs there... forever.

Before this started happening, I did notice a severe lag in the system as a whole, and I believe it's down to either of the two things:

1) I foolishly installed "CleanMyMac X" after noticing that my iMac was slowing down and the software has obviously done more harm than good and I believe it to be the culprit as to why I can no longer boot. (I know - bad idea!)

2) My Internal HDD is possibly failing and nearing the end of its life (see iMac Specs below):

iMac 27" (Late 2013)

3.5GHZ Quad-Core Intel Core i7

24GB RAM

3TB Fusion Drive (1.97TB Used)

NVIDIA GeForce GTX 780M 4GB GDDR5

Running: macOS Mojave

I've researched this issue extensively and tried many different remedies with no luck:

Booting in Safe Mode (doesn't Boot in Safe Mode at all)
Resetting the PRAM
Entering Recovery Mode & Repairing Disks
Unplugging from the Mains, Holding Power Button for 10-15 Seconds and Plugging Back In
This Method, although I haven't tried Verbose Mode yet (https://mrsystems.co.uk/blogs/news/too-many-corpses-being-created)

And now I've come to the following options:

Cloning my Mac's Drive via Disk Utility to an External HDD (to save all my important data externally)
Retrieving my Data from Backblaze (albeit there be 200 Files missing as the backup must've been interrupted from the constant slowing and crashing)
Reformatting Everything & Reinstalling the macOS (but of course - losing everything!)

Now, I've purchased a 4TB External HDD specifically for the purpose of creating a clone of my Mac's Drive on to it. In Recovery Mode, I have formatted the Ext. HDD to MacOS Journaled and attempted to start the "Restore" process. Somewhere along the line, my Macintosh HD has become an APFS Volume (assuming it was from the Mojave update). So, when I click "Restore", Disk Utility automatically converted the Ext. HDD to APFS too so both drives match. (I think that's what it's doing when it says below 'repartitioning target device'.

This is where the problem lies... I hit "Restore" and after about 10-15 seconds I receive this error message:

"Validating target..."

"Validating source..."

"Repartitioning target device..."

"Validating sizes..."

"Could not validate sizes - File too large"

"The operation couldn't be completed. (OSStatus error 27.)

"Operation failed..."

Any ideas what I'm doing wrong here? It doesn't make sense to me that a 3TB Fusion Drive is "too large" for a 4TB External HDD - or have I misunderstood? I've tried multiple times with the same result and it's really frustrating!

I was literally in the process of preparing to back everything up after some intensive video editing work over the past couple of weeks - then this happens. (Images attached for reference):

Again sorry for the long post - but any help or advice would be greatly appreciated!

Thanks!

iMac Line (2012 and Later)

Posted on Dec 24, 2018 6:36 AM

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Answer 1

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myaka

Level 4

2,783 points

Dec 24, 2018 7:01 AM in response to TreyD95

You could, in repair mode, install a new system on the "backup" drive. Then boot into it and see if the original drive mounts. If it does, you may be able to perform a finder copy of some or all files to the new drive.

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Answer 2

TreyD95 Author

Level 1

9 points

Dec 28, 2018 6:18 AM in response to myaka

Hi myaka,

Thanks for your reply! Installing macOS on to a separate EHD and booting from that works, which is great. My Internal Macintosh HD does mount and I can see all the files and - although slow - I can open/preview most of them.

I'm currently making a backup on my Macintosh HD to my 4TB EHD via Carbon Copy Cloner and it's unbelievably slow to transfer! It's been going 74 hours now and only managed to transfer 926GB out of 1.97TB.

Thought this seemed very odd and decided to try transferring a small folder (less than 1GB) to the BACKUP drive from the Mac HD and it took over 20 minutes for 977MB. Yet, transferring a 2GB folder in reverse ONTO the Mac HD transfers at normal speed.

Is this a sign that the internal HDD is failing?

I'm almost certain it's on its way out, even without formatting it and retransferring the files back on to it once the cloning is done. Considering purchasing a 2TB SSD and getting it swapped out if so...

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Answer 3

myaka

Level 4

2,783 points

Dec 28, 2018 7:08 AM in response to TreyD95

TreyD95,

It's probable that the drive has issues. What follows is a crap shoot: a - you could use Disk Utility to repair the drive, and risk losing it completely in the process (any continued access of a failing drive might speed its demise), or b - copy the files you simply cannot do without first, (risking that they are damaged by a drive that cannot read all its original data) and then attempting Disk Utility repair. It's possible that the internal drive can be resurrected.

If you are able to repair the internal drive, however, you absolutely must use a Time Machine drive for backups (or some other backup solution of your choice) to mitigate the impact of future drive failure. All drives fail. The only variable is when they will fail; some go early, some go late, and some go about when expected. Without a backup, your data may be irretrievable.

I'm not sure about the slow read-from but fast write-to speeds.

Was your internal drive nearly full? Drives that are at or near capacity can perform quite slowly/strangely and present problems merely because they do not have the space needed for the OS to perform maintenance and other tasks. That may be a culprit. 15% free space is a good rule of thumb. If close to capacity, a lack of free space might be part of the issue, although I'd expect it would still start up (quite slowly) if that was the only problem.

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Answer 4

TreyD95 Author

Level 1

9 points

Dec 31, 2018 5:09 AM in response to myaka

No worries, myaka! Like I mentioned, the Backblaze Backup seems to be missing the lastest 200 files (which from memory would be some of the most important), so recovery of that data would probably be one of my last resorts - but is always an option if it comes to it.

I'm thinking of taking it upon myself to order a Crucial 2TB SATA SSD to replace the old Macintosh HD: https://www.amazon.co.uk/Crucial-MX500-CT2000MX500SSD1-Internal-NAND/dp/B078C515QL/ref=cm_cr_arp_d_product_top?ie=UTF8

I've currently got Crucial RAM installed to the iMac and it's a brand I've trusted-well for the past 5 years. Would you say this model SSD would be a suitable replacement/upgrade from my original 3TB Fusion Drive?

I know there'd be 1TB less of storage, however, I'm looking to do a clear-out of some old files to hopefully bring that 1.97TB to a much smaller number - whilst retaining all important files - not forgetting to mention hopefully a significant speed boost across the system.

I tend to store a lot of RAW Footage & Files for my Video Editing & Photography work on External Drives anyways, so losing 1TB isn't such a big deal for me.

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Answer 5

myaka

Level 4

2,783 points

Dec 31, 2018 7:15 AM in response to TreyD95

Sure, Crucial is a known good brand. Recently added a Micron 2TB SSD to my ‘012 Mac Mini. I’ve put a few different brands of 2.5” SSDs in MacBooks without issue — not so difficult a process in the machines I’ve done, anyway.

Btw, to avoid your current predicament, you might consider a larger conventional drive as a Time Machine, preferably (for a MacBook, in particular) connected wirelessly. My other half rarely plugged in a usb Time Machine to a MacBook, so I attached one to a router to make them happen automatically over our home network. The most that can be lost that way is an hour’s work.

if you set Backblaze preferences to back up continuously, you might lose fewer files that way, also.

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Answer 6

TreyD95 Author

Level 1

9 points

Dec 31, 2018 11:41 AM in response to myaka

Awesome, glad to hear you've used multiple SSDs without any issues! Of course all drives can fail, but I feel obtaining an SSD over a default, spinning HDD would give me better peace of mind for my kind of work.

I only have the 1 iMac and no MacBooks, would the 4TB EHD that I'm currently using to clone the files off the Macintosh HD be a suitable drive for Time Machine backup? It has asked me a couple of times if I wish to use the drive for TM and for the time-being I've said 'No', whilst it clones all the files first.

The intention is to clone the files back on to the SSD (once it's fitted internally), then use the 4TB EHD as my Time Machine backup of whatever's on my iMac in future. Also, is there a way of setting my Time Machine to do 2 backups - then alternating between each backup as it overwrites? (Don't know if that makes any sense...)

I have set up Backblaze to backup continuously, but due to the large amount of video files (I shoot wedding films), the backup process slowed down significantly just before the Macintosh HD conked out.

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Answer 7

myaka

Level 4

2,783 points

Dec 31, 2018 2:33 PM in response to TreyD95

iMac -- of course -- have had MacBooks on the brain, it seems. I've placed a rotating drive and and two SSDs in three separate iMacs as well -- not for the faint of heart, imo.

Looks like you are on a good path to restoring the files you are able to recover. A time machine drive should be (rule of thumb, here) two to four or more times larger than what you want to back up. The larger it is, the farther back in time you will be able to look for files that have been deleted or changed. You will have to decide if 4TB is enough once you've determined how much you want to back up.

Your question about two Time Machine backups is a good one and makes great sense. it is wise to maintain a multiple backup strategy.

If you partition your backup drive into two equal segments, you can select each as a separate Time Machine, but I wouldn't recommend that: should the drive fail, there is a significant risk of losing both partitions and all your backup data.

That is why I have two physically separate Time Machine drives for each computer in my home. Attach the drives; next, in the Time Machine preference pane, select one and then the other -- the OS will ask if you wish to replace the first or use both. If you select both, it will alternate backups hourly. Two separate, simultaneous Time Machine drive deaths is quite unlikely -- like winning a national lottery.

Those employed outside the home sometimes maintain a pair of identical portable backup drives updated weekly (or some other regular basis) -- taking one to a place of employment and swapping each for the other every selected period. It's particularly useful should backup drives at home be lost through flood, fire, or theft. One could achieve the same thing with an oft-visited friend or relative (or convenient safety deposit box).

You may already be aware that Backblaze (which I also use) states that it will not back up Time Machine drives -- so don't expect that level of redundancy.

Hope all this helps -- and that I haven't misread or forgotten anything else!

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