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With APFS, Apple focuses on storage efficiency in its OSes

Lucas Mearian | June 20, 2016
The new Apple File System will span iOS, OSX tvOS and watchOS, but some question whether it's needed

APFS's snapshot and replication features, Handy said, are two important storage services that data center storage area networks (SANs) support. But he also cautioned that they're only as good as the second storage device to which they copy.

"If this is an OS for laptops..., then neither of these make sense, unless all the snapshots and replication are copied to the cloud. If that's the case, there will be many cases when these won't be helpful because of a lack of connectivity," Handy said.

Handy also questioned why Apple would need to create an encryption function in its file system when many SSDs today come native with the feature. "Roughly half of all of today's SSDs are already self-encrypting. It doesn't cost appreciably more," he said.

Apple did not respond to a request for comment by Computerworld on its new file system's features.

According to Apple's AFPS guide, the system allows users to choose several encryption modes for each volume in a container, including: no encryption, single-key encryption or multi-key encryption with per-file keys for file data and a separate key for sensitive metadata. APFS encryption uses AES-XTS or AES-CBC, depending on hardware.

In its desktop OS, full-disk encryption has been available since OS X 10.7 Lion. In iOS, a version of data protection that encrypts each file individually with its own key has been available since iOS 4, according to the iOS Security Guide. "APFS combines both of these features into a unified model that encrypts file system metadata," Apple's guide said.

In terms of SSD optimization, APFS -- like HFS+ on which it is based -- supports TRIM operations, which delete blocks of data no longer in use in order to free up capacity.

"On APFS, TRIM operations are issued asynchronously from when files are deleted or free space is reclaimed, which ensures that these operations are only performed once metadata changes are persisted to stable storage," Apple said.

Apple also introduced "Space Sharing" in APFS, which allows multiple file systems to share the same underlying free space on a physical volume.

"Unlike rigid partitioning schemes, which pre-allocate a fixed amount of space for each file system, APFS volumes can grow and shrink without volume repartitioning," Apple said.

Each volume in an APFS container reports the same available disk space, which is equal to the total available disk space of the container. The feature is similar to another used by enterprises called "thin provisioning," which uses virtualization to give the appearance of having more capacity than what is actually available.

Thin provisioning allows volumes to grow or shrink as needed, instead of creating fixed volume sizes as storage administrators once did.


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