NAS Time Machine verify does not finish

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NAS Time Machine verify does not finish

Time Machine backup to a Western Digital PR2100 NAS: This backup starts, but never finishes a verify (automatic process for NAS backups). Given enough time (hours), the verify will just stop (no error message), successfully do another backup, then gets stuck in verify again. This problem started just after upgrade to Big Sur. Another, nearly identical iMac, with exactly the same backup hardware and strategy, has no issues. Everything has been rebooted.

Apple claims that Time Machine works with this NAS, but various user notes point out that using a NAS for Time Machine is risky. I need a reliable solution....

Start a new backup -- will it just fail again later?
Stop using the NAS and buy more expensive direct plug-in drives?
Just let it run and hope that someday verify will complete?

Anyone else seen this problem, and hopefully fixed it?

Thank you! - Andy

iMac 27″ 5K, macOS 11.2

Posted on Mar 15, 2021 8:31 PM

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Answer 1

Best reply

Tesserax

Level 10

148,895 points

Mar 16, 2021 8:59 PM in response to alaz0

That "extended" verify process is, unfortunately, a harbinger of pending doom. At least that is my experience. As I mentioned, I have been using a Synology NAS for TM backups. It was flawless for over 4 years, but then I too, started to see that the verification process happened more frequently with each subsequent backup. Like you, it "hung up" around 75-80% done. This went on for about a month before I got the dreaded "your backup is corrupted" error ... so this may not just be limited to Synology, but other NAS manufacturers' devices as well. Could it be because of macOS Big Sur? Possibly as Apple basically has made significant changes to TM backup process since macOS High Sierra. If you want to get more details on what has evolved with TM, I suggest you head over to The Eclectic Light Company's website where you will find a number of interesting articles.

The bottom line for me, is that I stopped relying solely on using TM for my overall backup strategy. Instead, I primarily use Carbon Copy Cloner and only use TM as a secondary means. If you don't already, I suggest you consider other backup solutions as well.

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Answer 2

Eric--F

Community Specialist

Mar 16, 2021 2:41 PM in response to alaz0

Hello alaz0,

Thanks for asking the Apple Support Communities for help with your Time Machine backup.

Please ensure you are set up as described in this help article: Types of disks you can use with Time Machine on Mac - Apple Support

The article states the following information: "Important: You can back up from an HFS+ or APFS-formatted disk to an HFS+ disk; however, Time Machine can’t back up to an APFS-formatted disk. If you select a back up disk formatted as APFS, Time Machine offers to reformat it as HFS+.

If the disk uses the Master Boot Record (MBR) partition type, some partitions may not be available for use with Time Machine.

If your backup disk is on a network, the network server can use Server Message Block (SMB) file sharing. Your Mac must be connected to the SMB server when you set up Time Machine. After you select the network disk in Time Machine preferences, Time Machine automatically connects to the disk when it’s time to back up or restore your data.

Note: Some SMB and AFP disks from manufacturers other than Apple don’t support Time Machine. If your network uses an SMB or AFP disk, but the disk doesn’t appear in the list of devices available for Time Machine backups, contact the disk’s manufacturer."

If your drives meet the requirements in the article, please go through the troubleshooting here: If you can't back up or restore your Mac using Time Machine - Apple Support

Thanks and have a wonderful day.

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Answer 3

Tesserax

Level 10

148,895 points

Mar 16, 2021 2:53 PM in response to alaz0

I'm not familiar with this particular WD NAS, but have been using Synology NAS devices for years now. In my case, there are a series of set up steps to allow the Synology to support Time Machine backups. It's not an automatic process. Is there something similar with your WD? I can try downloading the WD user guide to see how its operating system works for this. However, if you already have a link to this document, please feel free to share it.

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Answer 4

alaz0 Author

Level 1

45 points

Mar 16, 2021 5:51 PM in response to Eric--F

Thank you, but I know most of that. The WD PR2100 has been working perfectly for 2 1/2 years on two different iMacs on the same network. Set up exactly as directed by Apple and Western Digital; worked right the first time. Now, this problem surfaced, but only on one iMac, the other continues to work perfectly. The setup is obviously correct; there is something wrong with the backup. On the failing iMac, TM prepares, backs up, and cleans up successfully every time. Then it always tries to verify; successfully verifies about 80%, then slows down and stops. It never finishes. That verify start, process fail, takes about one hour -- every time. Other than that, the backup file reads (so far) without problem. It is set up with SMB.

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Answer 5

alaz0 Author

Level 1

45 points

Mar 16, 2021 5:53 PM in response to Tesserax

Thank you. Please read my previous reply. This is not a setup problem -- it's been working fine for 2 1/2 years or so. There is something about "right now", either a backup corruption or a Big Sur problem (?). There is no error message; it just stops and quits after an hour or so.

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Answer 6

alaz0 Author

Level 1

45 points

Mar 17, 2021 4:50 AM in response to Tesserax

Sigh -- yes, I agree. In fact, I was heading for the same conclusion as well. It's frustrating, as I bought the NAS specifically to deal with a common backup system.... According to my notes, I already had a "corrupt" error once, some time ago, but thought it to be an anomaly. I'm guessing that the problem lies in the "sparse bundle", which puts an Apple formatting on top of a Linux/Unix formatting used in NAS drives. That always struck me as being error-prone. Apple does not verify direct plug in drives (e.g., Thunderbolt, USB) using Apple formatting. I've been thinking about alternative backups for the past few days, and will follow up on your suggestion of Carbon Copy, and will check The Eclectic Light Company site as well. Thank you for your response and straight shooting; I always prefer the truth over answers that I would prefer.....

For what it's worth, when I used home-brew, Linux based systems, I wrote my own backup program; not as user-friendly as TM, but solid and effective. However, the code does not work under Apple Unix, as two of the required commands (e.g., for symbolic linking) do not exist.

I very much appreciate your effort and time that you gave me. I will return the favor to the next user.... Thank you.

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Answer 7

alaz0 Author

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45 points

Mar 17, 2021 4:56 AM in response to Eric--F

Well, I linked to the Apple explanation of how to use TM on what disk format. The following is an exact copy of a key statement in that document:

"APFS or APFS Encrypted disks are the preferred format for a Time Machine backup disk. If you select a new backup disk that’s not already formatted as an APFS disk, you get the option to erase and reformat it."

The article that you cite does not agree with your statement referring to the same article.

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Answer 8

alaz0 Author

Level 1

45 points

Mar 17, 2021 5:05 AM in response to alaz0

By the way, for a NAS, the APFS preference is moot, as NAS operating systems typically use Linux-based formatting. Apple then applies a "sparsebundle" formatting over the top of the NAS disk formatting, and writes the TM files to that sparsebundle. It is my opinion that this is not an APFS issue, it's a sparsebundle bug that is the issue.

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Answer 9

Tesserax

Level 10

148,895 points

Mar 17, 2021 10:25 AM in response to alaz0

FYI ... When doing some investigating of corrupted TM backups to a Time Capsule (TC), which traditionally formatted the TM disk image (aka, sparsebundle) in HFS+, switched to APFS with macOS Big Sur ... although not automatically with existing sparsebundles on the TC. However, if either starting a completely new backup or erasing existing backups, all newly created sparsebundles were APFS ... so, I tend to agree with you that this could be a sparsebundle issue.

... and thank you for providing your findings as well. TM backups to NAS devices, is something I still haven't had a chance to investigate beyond looking at the backup process via the logs.

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NAS Time Machine verify does not finish

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