# What is Apple File System and Why is it Better than HFS+?
If you’ve been following the news from Apple’s latest releaseof macOS, you might have noticed some mention of Apple File System, or APFS. This is one of those wonkytopics that don’tget a lot of attention. Yet, it’s the core structureunderlying a user’s experience with the operating system.APFSwon’t be finalizeduntil 2017, but you can get a taste in the developer preview now available on Sierra.
### Differences and Improvements
To review quickly, a file system is the basicstructure an operating system uses to store and retrieve data. Different file systems take different approaches to this task.As computers have become faster, newer file systems have takenadvantage of the boostto offer new features and adapt to modern storage needs.
HFS+, the file system that ships with new Macstoday, is eighteenyears old. HFS, its progenitor, is older thanthe Tom Cruise bromance flick “Top Gun.”It’s sort of like an old Toyota. It still works(maybe surprisingly well), but it’s not winning any medals.
APFS isn’t so much an upgrade to HFS+ as it isa quantum leap forward … to the present. Though it’s a majorupgrade for Apple users, it seems mostly like Apple is catching up to other systems, rather than overtaking them.Nevertheless, the update isn’t a day too soon.
APFS uses a scheme called copy-on-write to make instant clones of duplicated files.Under HFS+ when a user duplicates a file, every single bit is copied. APFSinstead creates a clone by manipulatingmetadata and allocating disk space. However, no bits are copied until the cloned file is modified. As the clone diverges from the original copy, those changes (and only those changes) are saved.
Copy-on-write also improves data integrity.Under other systems if your volumeunmounts with overwriteoperations pending, you might find part of your file system out of sync with the rest. Copy-on-writeavoids the problemby writing changes to freedisk space instead of overwriting old files. Until the write operation successfully completes, the old file is the canonical version.Only when the new file is successfullycopied is the old file purged.
Snapshots are a major upgrade and are brought to you in part by copy-on-write architecture. Asnapshot is a read-only mountableimage of a file system at a point in time. As the file system changes, only modified bits are saved. This can make backup simpler and more reliable.Considering the ungainly disappointment of hard links that Time Machine has become,this could bea major upgrade.
### I/O Quality of Service
You may have seentheterm Quality of Service (QoS) inyour router’s setup instructions. QoS prioritizes bandwidth usage to avoid slowing down prioritytasks. On your router it employsuser-defined rules to giveselectedtasksthe most bandwidth. Reportedly, Apple’s QoS would prioritize user operations such as active windows. Background taskslike Time Machine backups would get demoted. So, maybe less beach balls?
In a post-Snowden world, encryption is all the rage. And more and more Apple is emphasizing the security of its systems. Built-in, strong encryption comes as no surprise. With APFS, Apple is incorporating a more nuanced encryption scheme than its current, whole-disk-or-nothing approach. Users can useasingle key to encrypt all theirdata or use multiple encryption keys to lockindividual files and folders separately.Of course, you could also encrypt nothing, you devil-may-care rascal.
Flash storage optimization has been listed as a headline feature of APFS, butthe implementation isn’t thrilling. Rather than taking advantage of theirunusual degree of system integration, Apple has insteadshifted some of the functions typically handled by the SSD’s chips to the OS. It’smore like the file system is aware of SSDs rather than optimized for them.
Logical partitions on an APFS drive can dynamically resize themselves. Users need only specify the number of desired partitions. The file system then works out disk allocation on the fly. Each partition only occupiesdiskspace that it’s using to store files. The rest of the disk space is up for grabs by any partition. It’s neat, but it’s a lot more like meta-folders than anything else.
### Conclusion
Does this matter? For devs and power users this is awesome. For casual Mac users there shouldn’t be much outward difference. And while the upgrade is great, there are still some missing pieces. Native compression is notably absent, as is checksumming on user data. Of course, anything could change by 2017, so watch this space.
