Moving Photo Library to a NAS

I’m curious if any of you have experience moving your Photo Library onto a network-attached storage device?

To offer some background, I have a 1.4TB photo library, and I’ve had it on an external RAID drive for several years. But that hardware is dying, and its software is lousy and often non-functional. So I bought a 4-bay Synology NAS, and I have successfully moved all my Time Machine backups to it, which is explicitly supported by both Apple and Synology.

I also wanted to move my Photo Library to it, but officially Apple doesn’t recommend it due to risk of data loss:

This guy goes into a lot of detail about where it is and is not safe to store a Photo Library, and he also says no to NAS:

But nowhere do I see an explanation about WHY it’s not safe. Only “Storing your library on a network share can lead to poor performance, data corruption, or data loss.”

Where I see valid concerns are:

  • in a synced folder, such as Dropbox or iCloud Drive, where syncing it to another location could confuse and corrupt the library
  • on a file system that is not HFS+, since I believe that the integrity of the library has been written in such a way that it depends on the journaling and other features of this specific file system it resides on
  • in a shared folder, where there’s a risk that two users may try to access (and therefore modify) the same library at the same time, which it’s not designed to do.

But none of that rules out NAS strictly. I will never put it in a synced folder or share it with anyone, and I can make sure it’s HFS+.

Another concern is that network storage will be slow. Well, that’s my problem to deal with.

And yet another concern is that disconnection of the network drive could lead to corruption. But I don’t buy that argument. For a reason that I don’t understand, my external Lacie RAID drives have been randomly going offline on a regular basis for YEARS. Then Photos says “Photos needs to Quit because the library has become unavailable.” Then I restart the drive, restart Photos, and everything is always fine. No corruption, no rebuilding. MUCH better than the old iPhoto days.

Nonetheless, this guy found a way to do it that adds a layer of safety that seems hard to dispute. He creates a sparse image on the NAS, mounts it locally on the Mac, and puts the library in there:

There is a least one commenter in there who is adamant that it’s a bad idea. But he seems to be nothing but a zealot with an Apple recommendation and no real knowledge. And some of the advantages of this approach are that you can force the file system on the sparse image to be whatever you want, independent of the file system the image lives on; and secondly, the image can only be opened and mounted in once place at a time, ensuring that it won’t be opened by two users at once.


I tried his idea, and have had it up for a couple weeks. It’s lost connection a couple times, but recovery is fine, just like with an external drive. Everything seems to be fine.

But I’m not sure if I’m living dangerously or doing just fine, thank you. I’d love to know if you guys have field experience doing this and what you think?

I’d offer my long-time experience of using a sparse disk image on a Synology drive as an hourly backup destination, over Wi-Fi no less, but I don’t want to be called “some guy” or a “zealot” if you don’t believe me.

I think @dave1 was saying that the sparse image approach naysayer was the person who didn’t seem like a technically reliable source. :slight_smile: So please do share your experience!

Adam is right! The “naysayer” was just repeating the generic Apple guideline and shooting down what might have been a perfectly safe solution without adding any useful technical or empirical input. In fact, if you read that thread, it’s exasperating to hear this sparse image idea getting summarily dismissed.

So please do share your experience!

Thanks for clarifying. :slight_smile: I use Carbon Copy Cloner to back up physical hard drives to sparse disk images that live on a Synology NAS on a several-times-a-day basis. (hourly and 3x day) CCC mounts the dmg files across the Wi-FI network from the NAS, then unmounts them when finished. I’ve been doing this since May of 2018 (based on the creation date of the .dmg files.)

I’d say that it works nearly flawlessly. I say “nearly,” because if other network activity is causing congestion, CCC will report that the disk is damaged and needs repair. I’ve never had Disk Utility find any trouble with the image when this occurs, which has maybe happened 4 times this whole year (and only occurs if bandwidth is severely constrained thanks to FaceTime.)

I’ll be surprised if it doesn’t work in your scenario. The only caveat I can think of is that you’ll want to make sure the virtual volume is mounted before launching Photos. That’s the slowest part of the operation across the network and I could imagine a scenario where the app times out waiting for it, particularly since it’s probably untested given the “unsupported” party line.

Thanks for that great reply!

Aha, good idea. I still have a separate external drive for that purpose, but consolidating that onto the NAS sounds appealing. But I have question: in the event my internal HD dies, the goal would be to boot from the CCC image and, when the new drive arrives, copy from there back to the new/blank internal drive. Can you do that from the NAS? Can a blank Mac detect a “NAS disk image” as a boot drive?

I have not had that problem. And I never seem to have to mount the disk image. I think Photos automatically mounts it when launched, but I will check that when I get a chance.

One more note just for the record… While Spare Image + NAS has worked great for you for CCC backups, that doesn’t necessarily imply that it’s safe for preventing the “data corruption, or data loss” Apple warns about for the Photos Library.

So I’m definitely still interested in knowing if anyone has reliably kept their Photos Library on a NAS…

I have no idea, I’m not imaging my boot drive to the NAS. But Bombich Software has excellent support so you might drop them a note.

I’m 99% certain that you would not be able to. You would have to do something like:

  • Boot the Mac into recovery mode (Internet recovery if the recovery partition isn’t available)
  • Install macOS from recovery mode
  • Install CCC on the new system
  • Use CCC to restore the system.

I don’t know if you will be able to restore the system volume, since you will be trying to overwrite the running system (which is never a good idea).

If you want to use a NAS for a whole-system backup, I would recommend creating a bootable device (maybe a flash drive with a minimal OS installation) with CCC installed. This way, you could boot that and use it to completely reimage the Mac’s storage from the NAS image.

Years ago, when I was making backups with Retrospect (and a tape drive), I did this. I had two hard drives in the computer. One had my running system. The other had two partitions - my application data and a minimal “emergency boot” system with macOS, Retrospect and not much else. I could boot it in order to restore the primary system partition from a backup (which I actually did once when a glitch in Tech Tool Pro clobbered the volume).

My method is slightly different:

Install macOS from recovery mode, but when asked about migration, use the CCC clone as the source for migration.

While this is off topic to my main post, the useful tangent about creating a bootable image to a NAS came up, so I did a little research on Carbon Copy Cloner, which I do use.

The short version is that, for reasons that I don’t totally understand, CCC does not recommend backing up bootable/system disks to a NAS:

For example, we do not recommend backing up macOS system files to a NAS; there are simply too many logistical and reliability concerns with this configuration. Below we explain how to back up your data to a network volume, then we describe some of the limitations and performance expectations of this solution.

Note on bootability: If you require a bootable backup or if you ever need to restore system files, you must use an external hard drive enclosure attached directly to your Mac to create a bootable backup.

Too bad. I will probably inquire for more technical detail on that recommendation since, as you have already learned, I don’t take no for an answer that easily :slight_smile:

One does wonder, however, if have given any consideration to backing up to a sparse image located on a NAS…

This is because NAS devices (especially image files on NAS devices) can’t be used as boot devices, no matter how you make the backup.

(Once upon a time, you could configure a Mac to boot from a NetBoot server on your LAN, but that is not the same as an image file on a NAS. And modern Macs don’t have this capability.)

If you clone your system to an image file (wither on a NAS or elsewhere) instead of an external drive, then the backup image won’t be bootable. You will therefore need to boot from something else in order to restore your files. And since you can’t overwrite a running system, that something else can not be the same storage device you want to restore your volumes to.

You can use the recovery volume to reinstall macOS and then restore your documents/apps from the network volume using Migration Assistant or CCC, but you can’t restore the system volume that way.

I’m sure you could install macOS on an external volume (a third volume, in addition to the Mac’s internal storage and your NAS), install CCC on it, boot from that volume, and then use it to clone the NAS image to the Mac’s internal storage, but that’s a bit too complicated for most users. And if you need an external directly-attached storage device, you might as well just clone your system directly to it and simplify everything.

I suppose you could clone the NAS image file to a portable disk, connect that to the Mac to boot from, and then clone onto the Mac’s internal disk from that using itself as the source.

Not that that’s particularly practical (you could have just cloned to that portable storage in the first place and forget about the NAS), but I guess it would work if you somehow considered the NAS mainly as extra insurance, i.e. you only clone from it in a total loss scenario. From my own experience, I know trying to clone onto the running system is a bad idea (unsurprisingly), but cloning from a running system has not been a problem (at least not using SD, haven’t used CCC in years I have to admit).

So, I got the reply from Bombich / CCC that I (and some of you) were basically expecting (essentially “no”):

The macOS can not boot from a disk image, therefore it is not possible to keep a bootable disk image.

We have suggested in the past the ability to make complete backups to a disk image, then potentially restore them to a drive, boot from the drive, then restore, but changes in the macOS and the move to APFS have made that less reliable.

To be clear, you can try that, it might work, but I would never consider it bootable, and I would not use it as a primary backup.

Too bad. Especially since the Internet Recovery feature built into all modern Macs is essentially an even more sophisticated version of what I’m looking for. Plus, the Mac already has the ability to restore from a network-mounted Time Machine backup. So unless I’m missing something, it wouldn’t be hard for the option-boot feature to access Samba drives, if Apple wanted to add that feature…

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Bummer. :frowning:

I agree it would be real nice for troubleshooting if you could use a mounted network share or even an image on a mounted share to boot or restore from. Since on the new AS Macs TDM is being replaced by some fancy SMB sharing anyway, it would feel like such network sharing could also be exploited the other way around to boot or restore a Mac.

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Hi folks,

Mac backup to a Synology NAS is technically off topic to this thread. But since it came up earlier, let me share this.

It looks like Synology is working on not only a Mac backup solution but possibly a bare metal restoration capability. I’m not sure technically how they will do it. But after watching lots of their videos, it seems clear that they’re eager to dominate this space and provide that level of functionality.

This link takes you to what’s coming in 2021 specifically for Mac backup.

I will be watching it closely!