Apple APFS Synthesized Disk Performance Sucks

[Robotron2k84]

Why? Because it’s a crap-sandwich of about ten different layers of abstraction between containers, encryption, data overlays, snapshots, sealed volumes, VM and recovery volumes, mirrors and SIP protection.

It may look uber-slick, but it’s uber-garbage!

If you want a real head scratcher, why does system performance degrade as the disk is filled and emptied? If you have a time machine drive attached or ever activated time machine, you have to checksum APFS snapshots on the fly for the boot volume.

What the crap? APFS is awful beyond comprehension.

If you want to save yourself some headaches, learn about “tmutil” and disabling local snapshots. There isn’t much you can do beyond that to improve boot volume speed, so head into the recovery partition and disable SIP and secure boot, image your disk onto an external SSD and boot off that. Externals that aren’t TM volumes won’t automatically snapshot and screw the pooch.

Apple, WTF?

[squeeze]

As a loooooong time Apple user and having purchased a new LaCie external drive (not installed yet) for use as a time machine and files on my iMac; I sure wish I knew what you are talking about. Your knowledge is light years beyond me; but thanks.

[yellowsulphur]

ZFS

[Robotron2k84]

What’s going on is that snapshoting is now the default in MacOS 11 and 12, and it’s getting to be a major pain.

I was helping my relative troubleshoot why it was taking hours to copy a gig or so of data from one folder to another. I honestly thought there was some hardware malfunction.

APFS doesn’t just copy files from one place to another anymore, it snapshots and then does copy-on-write to allow for supposedly quicker moves and fewer write cycles on SS media. Total BS!

The Achilles heel of this file “system” is if you write a lot to the volume and then delete, several times. It creates a snapshot every time the disk is being filled and only truly wipes the data when it comes time to overwrite blocks.

This has the effect of having to keep track of literally hundreds of potential snapshots in memory and linking them all through about three kernel threads to effect a “view” of a single data partition.

It causes the machine to become CPU-bound just trying to write to the disk, and quite literally turns a bus-mastering and queuing disk controller into the equivalent of an ‘80s host-driven ESDI drive. Every bit of data now has to traverse the kernel at least four times (for a simple volume) with side-channel mitigations enabled.

It’s a f’ing disaster and I can’t believe that this is an actual serious OS. It makes MS look like rockstars by way of comparison.

Junk!

[arrix]

Shadowing or snapshots shouldn't slow your SSD that much. There must be something else going on.

[Robotron2k84]

In a normal OS, snapshotting and working with clones involves almost no overhead, save for the extra space required for the delta inodes. The user above that mentioned ZFS (or WAFL, BTRFS, etc) are all solid choices, but not supported on boot volumes. I kinda wonder if the UFS kernel driver is shipped in 11/12. Might try to see if I can get a true Unix boot volume.

In Apple’s case, they architected the APFS filesystem to store granular block-level deltas, but then make no use of that granularity, anywhere in the OS. Not even in timemachine, which was ostensibly the reason to move to snapshots for the boot volume. The deltas aggregate over time and there is no method to clean them up. The slowdown then happens because all I/O has to now go through code in the kernel that layers all the different parts of the volume and all the snapshots together in real-time.

It’s poorly designed and the only way to alleviate the incorrect behavior is to not use snapshots on your boot volume. Hence the comment about booting off of external media all the time.

It’s sadly just another step in the path that Apple keeps going down: poor design because Tim Apple really doesn’t understand computers, and drives products on image and gloss, alone. When Apple said goodby to OSX, they threw the good out with the bad and what’s left is just mediocre, at best.

Thinking about starting a GFM to clone Steve Jobs.

[Robotron2k84]

One more turd in the punchbowl to watch out for. When your APFS boot volume has > 90% utilization, even if it has a TB free, the OS will NOT let the system snapshot the boot volume, specifically for TM backups.

This is a completely silent failure and nuking the local boot volume snapshots will NOT solve the problem and you need to get below 90% to successfully perform the backup.

All, please monitor your backups on 11 and 12 if your disk is close to capacity, percentage-wise.

Unbelievable.

[Robotron2k84]