Why Time Machine is broken

Why Time Machine is broken

Summary: Mac OS X's Time Machine backup is the easiest and cutest backup in the industry. But for many its performance stinks, forcing people to turn it off. Why?


Mac OS X's Time Machine backup is the easiest and cutest backup in the industry. But for many its performance stinks, forcing people to turn it off. Why?

A great idea Few people back up their data because it's work. You have to choose what software and hardware to use, buy it, configure it and then hope it works when you need it.

Time Machine solved that. Part of Mac OS X since Leopard it automagically backs up the stuff you care about.

It's easy: plug in a 2nd disk - USB or FireWire - to your Mac and it asks if you want to use that disk for Time Machine. Click yes and you're good to go.

TM backs up hourly. It keeps hourly backups for 24 hours, daily backups for a month, and weekly backups for all previous months thereafter. But it isn't an archive because it kicks old stuff out when the disk fills up.

To restore a file click on the menu bar TM icon, choose "Enter Time Machine" and you get the nifty interface:

[image courtesy Apple Inc.]

(image courtesy Apple Inc.)

Civilians are always blown away by the Time Machine interface. It looks great and it works intuitively.

Problems People I support here in "the real America" started complaining about Time Machine's impact on performance. Spinning beach balls, long pauses, even system crashes.

I noticed it too and using TimeMachineEditor I cut the hourly schedule to once a day. It helped but finally I turned it off. I run daily non-TM backups and didn't need the grief.

But it made me wonder what was going on under the hood. Several factors contribute to Time Machine's poor performance.

  • If a single block changes in a large file, the whole file is recopied. Expensive if you routinely work with large files.
  • If you keep thousands of e-mails in your inbox - and I do - each Time Machine backup has to create thousands of hard links to each email.
  • At the same time it has to break thousands of hard links up because the Time Machine starts deleting hourly backups after 24 hours.
  • Hard links aren't costly in most Unix systems, but they are in Mac OS - each requires a couple of disk I/Os which kills performance.
  • While new hard links are created, the system locks the file system B-tree, locking up the system.

The Time Machine engineers tried to make this overhead inconspicuous. If you're a light user you won't see much impact.

But if you receive and keep a lot of e-mail, download and keep a lot of content or perform large-file I/O intensive work - video, Photoshop, music - you'll find that Time Machine has a noticeable and perhaps unacceptable impact on system performance.

The Storage Bits take Casual Mac users are fine with Time Machine. But with Macs owning over 70% of the high-end PC market it is power users that Apple should worry about. They need Time Machine protection but they also need performance from their premium priced machines.

Time Machine's public face is wonderful. The intentions behind it are excellent. But the underlying infrastructure of hard links and complete file copies is incompatible with the high-end PC market.

Modern file systems use low-overhead copy-on-write snapshots, checksums and byte level change records to minimize storage I/O. TM's architecture, on the other hand, maximizes expensive disk I/O which kills machine throughput.

The obvious solution is for Apple to go back to their original plan to use ZFS as the new Mac OS filesystem. NetApp, whose patent suit against Sun scared Apple off, has settled with Oracle and would, no doubt, do likewise with Apple.

Bottom line: HFS+ isn't up to the job of meeting 21st-century file system needs. Apple needs a new foundation for the Mac OS and they need it now.

Courteous comments welcome, of course. Apple has a nifty intro to Tima Machine here.

Topics: Apple, Hardware, Operating Systems, Software, Storage, PCs

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  • You're making that up, right?

    [i]You have to choose what software and hardware to use, buy it, configure it and then hope it works when you need it.[/i]

    You have to be joking; pretty much all the backups out there all you do is plug it in, the software loads (if you click OK) and it configures the backup for you.

    now, where do you add this "second disk" to on a Mac...?
    John Zern
    • Plug the second disk into a USB or firewire port.

      @John Zern

      Not exactly the Way of Mac, but it is the best option.
      Lester Young
    • RE: Why Time Machine is broken

      @John Zern Uh, yeah. You've never used Backup Exec or Retrospect with an LTO3 or 4 system have you?
      • RE: Why Time Machine is broken


        Time Machine isn't a replacement for Backup Exec or Retrospect. Those are server backup products. Time Machine is a desktop product.

        However the Sonicwall CDP does better than the time machine, backing up files in real time as changes occur and without any noticable impact on performance.
    • RE: Why Time Machine is broken

      @John Zern
      Really? There's a 1-button backup that will automatically backup all changed files every hour? Does it have a name?

      Robin Harris
      • Agreed. Where is it?

        @Robin Harris

        Let us know your opinion on qRecall.
      • Lots of one button backups out there

        you just have to look around at other, NON-APPLE hardware

        And is backing up changed files every hour all that important? Just backup the changed files every night is fine. And it sounds as though If I have something that would do it every 45 minutes, that would definately be better then Time Machines, as it only does it every 60 minutes.

        And where does that second disk go?
        John Zern
      • RE: Why Time Machine is broken

        @Robin Harris
        Try getting Apple to use "rsync" in Timemachine -- does great backups locally, on the LAN and across the internet with "ssh"
      • RE: Why Time Machine is broken

        @John Zern

        Actually, John... backup once a week is good enough, it's unlikely that a home user is going to have that many things changed that are important that they have to backup every night.
    • RE: Why Time Machine is broken

      Adding drives to a Mac? I have a 1TB bus powered Firewire 800 and two 500GB bus powered USB drives. In addition to that I have a 2TB Time Capsule with another 500GB drive attached to that.

      I agree that HFS+ is dated and Apple should be doing something about that, but Time Machine is still a very handy tool. I just don't use it as my only backup tool. I also use SuperDuper to do a (bootable) backup every other night to the FireWire drive and manually backup a few critical files to my .me account.

      Time machine works undetectably in the background and I'm using it wirelessly with a 2TB Time Capsule (I upgraded the drive). It backs up my 1TB internal drive (upgraded that too) and two 500GB data drives. No slowdowns that I can detect on my mid 2009 MBP. The only way I know it's running is if I notice the icon in the menu bar spinning. No spinning beach balls, no crashes of any kind (with the exception of Flash, but even that's stopped with Adobe's latest revision). I just make it a point to keep all of my software updated and avoid "Haxies" like the plague.

      I had a very nasty HD crash back in '97 or '98 and lost a lot of irreplaceable data. I learned my lesson and now take my backup regimen very seriously.
  • Hmm, no problems on Windows!

    Windows has a [b]far[/b] superior solution. With the combination of VSS and Restore Previous Versions (which just works), you get most of the benefits of a backup even while you aren't connected to your second disk. Take your OS X machine on the road for 2 weeks? Guess what, you don't get a [b]single[/b] backup for those 2 weeks. Inexcusable.

    Of course when your Windows machine is connected to a second disk or a network, the built in backup backs up to the external data store but guess what, Restore Previous Versions [b]still[/b] works exactly the same.

    No, the Windows interface isn't as flashy but that is because in this case, you don't actually want flashy, you want familiar. Why do I need to use a different interface to restore my files? OS X forces you to. Windows gives you the familiar Windows Explorer interface. Intuitive. Easy. Efficient.

    Time Machine is a [b]perfect[/b] example of where Apple goes for form over function. While you guys are so impressed with fancy backgrounds and neato names, our Windows "Just Works". :)
    • RE: Why Time Machine is broken

      @NonZealot Nope, no problems with Restore on Windows at all...
      • irony

        @athynz I've never had problems with window's System Restore functions...

        ...instead, I've had problems with their updates, which then REQUIRED restores. <.<

        As for my files and data? well... I don't trust windows with it, and have my own backups.
    • And the da award goes to....


      Shadow copies, as cool as they are, are not backups. By default, lose your disk, lose your shadow copies.
      • RE: Why Time Machine is broken


        Never had any issues and rarely ever had to use Windows System Restore. Secondly if your hard disk fries you're using inferior hardware. I've only had this issue twice both were Seagate which I never used again but is a standard on all Apple's. Makes sense why you need to back up so often with your ticking timebomb HD. Hitachi and Western Digital FTW! I love owning a regular PC I can do whatever I want with instead of the "Apple Approved Options" you're stuck with.
      • RE: Why Time Machine is broken

        @audiodiablo, I don't know where you heard that Apple only uses Seagate drives but that's just not correct. Apple uses drives from all manufacturers. I share your mistrust of Seagate drives but out of the four drive failures I've experienced since about 1987, there was one Seagate, one Maxtor, one Quantum Fireball and most recently one Western Digital. And the Seagate was a 20MB model so that was a LONG time ago. I did have a Seagate drive start making clicking noises a few years back but it never actually failed. I think that was an Apple OEM drive but if I recall correctly, that was the only Seagate I ever pulled from a Mac. I did remove a 500GB Seagate from a Time Capsule and replaced it with a 2TB WD, but the original drive worked fine and is happily living in a friend's Gateway.
      • RE: Why Time Machine is broken

        @People not if you are using offline folders and a file server that has VSS enabled.
    • RE: Why Time Machine is broken

      Sounds great but what is VSS? Which windows?
      • RE: Why Time Machine is broken

        @pauliusp i think visual store system and system restore have been there since XP
      • VSS is Shadow Copy, it was introduced in Vista...

        @pauliusp VSS is Shadow Copy, it was introduced in Vista, and it [i]isn't[/i] backup because it's on the same drive as your data. You'd still want to purchase a 3rd party package for backup.

        Time Machine is OK for client side backup, but there are better backup solutions available, with more options to choose from, including many free GUI frontends for rsync (which is what Time Machine is) such as Carbon Copy Cloner.

        Apple gives you a simple and user friendly interface to a UNIX utility, but it is limited. If you're a keyboard jockey, you can get a lot more out of rsync than what Apple offers.

        If you're on the road, there are several companies that offer services that integrate with Time Machine for syncing over the web, including Apple's own Mobile Me service.