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I am using High Sierra (10.13.2, all updates in, including the one for Meltdown). When I do one of my regular checks for disk health using the first aid in Disk Utility the whole process is (1) incredibly slow and (2) recently freezes my laptop altogether. Given that I have a a 500GB SSD with 160 GB space, I am well surprised both by the drop in performance and now, by the fact I need to restart my laptop.

In the latest shenanigans disk utility was so slow that it passed the point when the screen goes off, and after that it was impossible to turn the screen on again (the mouse pointer was responsive). Am I to assume that disk utility takes, say, 30 minutes now to run and during the check the computer will be utterly unresponsive? How do I speed this process up, if at all possible?

Disk Utility always ended up causing the laptop to freeze for a small while, but here we are talking an abnormal amount of time.

  • It's hard to tell if reasonable is 30 minutes without knowing how many volumes in APFS you have and how many snapshots each volume maintains. For a main macOS install - it's not unusual to have 5 volumes and 20 snapshots of the main volume. – bmike Jan 13 '18 at 14:43
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On HFS+, something is wrong for a less than TB sized Apple SSD to take 30 minutes to run a check. On APFS, it's slightly more complicated. Depending on how many snapshots you have, this might be normal but you'll need to get some details to know.

If you're on APFS - you'll need to look at the logs or enter to the command line to determine how many snapshots of the volumes exist. If your fsck is taking 2 minutes to run, but you have 30 snapshots - there goes an hour on a full fsck and no "problem" other than perception. On the other hand, an hour to check one snapshot and you're back in "this is taking longer than usual by dozens of times".


I would get all the files backed up before you try to run the repair since a slow check almost always happens when storage is failing (but doesn't always correlate and certainly doesn't cause the failure itself).

At this point once you're backed up, you can take the fast path or the slower one:

Fast path - download the OS installer you want (High Sierra or whatever) and wipe the drive. When you are booted from an external USB, repair the drive twice to see if the second pass is faster than the first.

If you have issues with a wiped / empty drive - you can seek hardware service knowing that your data is backed up.

The slower path is to still boot from another drive and just repair the drive. You might get a good read of the speedup or if your data and drive really take 30 minutes to check all the system structures.

Booting to single user mode also might help in the short term and run /sbin/fsck -fy twice from the black screen to see if trimming the free blocks can help the storage allocate storage more efficiently.


On my MacBook that's been running High Sierra for quite some time, the single mode filesystem check reports 19 snapshots and that matches up with Time Machine:

tmutil listlocalsnapshots / | wc -l

The above list of local snapshots belonging to Time Machine counts 18 lines of output. None of the snapshots are more than an hour old as my Mac runs normally on power, with the external time machine destination connected so the snapshots cover the last day or so. I have seen it grow to 35 snapshots when I'm traveling and not doing hourly backups to the main time machine destination drive. They clean themselves up as far as I've observed in all cases.

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    fsck -y fills me with terror to be honest – user1256923 Jan 12 '18 at 17:28
  • @user1256923 It should if you don't have a backup. Filesystem check means throw out all the files that are corrupting the structure of the disk. It's a little like the metaphorical "baby out with the bath water" in that it will empty the tub if needed without pausing or asking. – bmike Jan 13 '18 at 2:12
  • I have a whole host of backups, and I regularly check for disk health both at the filesystem level and the hardware level. In all cases I get exit 0, though I have to wait for it. Thus having to effectively take a whole working day off to see if I can sort (no guarantee there) the issue just makes me resentful towards Apple rather than motivated to go through the non trivial disruption, especially because I suspect APFS and the Meltdown fix to be the actual culprits here – user1256923 Jan 13 '18 at 8:50
  • Just to be clear, after upgrading to High Sierra/APFS I noticed a very noticeable slowing down of Disk Utility -- yet it was still acceptable. Now after the Meltdown security patch things are now glacially slow with Disk Utility. – user1256923 Jan 13 '18 at 8:53
  • I'll add details about APFS snapshots, each update does add a snapshot, which doubles the check time for the volume that was snapshotted (but doesn't add incremental times to check other snapshots). Perhaps you just have 10 snapshots and nothing is really "wrong" @user1256923 – bmike Jan 13 '18 at 12:43

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