Flash storage and Fusion Drives are two different types of computer storage technologies. Flash storage refers to solid-state drives (SSDs) that use flash memory, while Fusion Drives are a hybrid drive technology developed by Apple that combines a hard disk drive with flash storage.
What is flash storage?
Flash storage is a type of solid-state drive (SSD) that uses flash memory to store data. Flash memory is a type of non-volatile memory that can be electrically erased and rewritten. Unlike traditional hard disk drives that use spinning magnetic disks, flash storage has no moving mechanical components.
Some key advantages of flash storage include:
- Faster read and write speeds – Flash storage can read and write data much faster than traditional HDDs.
- Lower latency – Flash memory has microsecond latency compared to the millisecond latency of HDDs.
- Higher reliability – Flash storage is less prone to mechanical failures or damage from drops/shocks.
- Lower power consumption – Flash drives consume less power than HDDs.
Common examples of flash storage devices include USB flash drives, SD cards, and solid-state drives (SSDs) used in computers. The most common formats for flash storage are SATA and PCIe. SATA SSDs can replace traditional hard drives, while PCIe SSDs connect directly to the motherboard via a PCI Express slot.
What is a Fusion Drive?
A Fusion Drive is a hybrid storage technology developed and marketed by Apple. It combines a traditional hard disk drive (HDD) with a NAND flash storage drive, with the goal of providing the large storage capacity of HDDs along with the performance of flash storage.
Specifically, a Fusion Drive consists of a hard disk drive and an integrated solid-state drive (SSD) which is referred to as the “flash storage.” The flash storage typically ranges from 24GB to 128GB in capacity, depending on the model.
The key characteristic of a Fusion Drive is that the HDD and flash storage are presented as a single logical volume. The operating system and applications see it as one single storage device.
Behind the scenes, the Fusion Drive uses a heuristics-based algorithm to determine which files and applications should reside on the faster flash storage, versus the higher capacity HDD. Frequently used files and apps are kept on flash, while infrequently accessed data is stored on the HDD.
This allows the Fusion Drive to offer both speed and large storage capacity in a single drive. For most everyday uses like booting, launching apps, and file access, the Fusion Drive will tap into the performance of flash storage. But it can also hold a user’s entire media library, documents, and other files on the larger HDD.
How is flash storage used in a Fusion Drive?
The flash storage component of a Fusion Drive acts as the faster, intermediate storage layer between the apps/OS and the larger HDD capacity. Here are some of the key ways the flash storage is utilized in a Fusion Drive:
- Caching – Frequently accessed data like boot files, applications, and commonly used documents are cached in flash storage for faster access.
- Swap space – The flash storage acts as dynamic swap space to hold temporary data as needed, improving performance.
- Metadata – File system metadata is stored on flash, enabling faster lookup and access of file directory information.
- Future writes – Data about to be written to disk is staged in flash first before being committed to the HDD.
- Data prioritization – The Fusion Drive software monitors usage patterns and keeps high priority data on flash storage.
By leveraging the strengths of both HDD capacity and flash performance, Fusion Drives aim to optimize storage speed and responsiveness. The flash storage plays a key role in boosting performance.
Key differences between flash storage and Fusion Drives
While the flash storage component is an integral part of Fusion Drive technology, there are some key differences between standalone flash storage and Fusion Drives:
| Flash Storage (SSDs) | Fusion Drives |
|---|---|
| Consists purely of flash memory with no HDD | Hybrid drives combining HDD capacity with flash memory |
| Available capacities typically up to 4TB for consumer drives | Total capacities up to 3TB in iMacs, higher in Mac Pros |
| All data resides on flash memory | Data is tiered between flash memory and HDD automatically |
| Optimized purely for speed | Balance of speed and large capacity |
| Higher cost per gigabyte than HDDs | Lowers cost compared to pure SSD solutions |
The key takeaway is that flash storage like SSDs offer pure flash memory and optimized speed, while Fusion Drives use flash as a complement to HDD capacity to deliver balance and flexibility. The integration happens below the software level.
Can you build your own Fusion Drive?
While Fusion Drives are sold as integrated units, it is possible for advanced users to build their own DIY Fusion Drive using an HDD and SSD. This involves the following steps:
- Acquire an HDD and SSD of appropriate capacities
- Install macOS and connect both drives to the computer
- Use the Disk Utility app to format both drives
- Create a logical volume group that combines both drives
- Enable the Core Storage Fusion Drive feature in Terminal
- Reboot computer and the drives will show as a single Fusion volume
Building your own Fusion Drive lets you pick your preferred drive capacities and potentially save some money compared to pre-configured Fusion Drive upgrades. However, it is a more advanced process requiring command line configuration. The supported drive combinations and stability may also not match Apple’s integrated Fusion Drives.
Fusion Drive considerations
For those considering a Fusion Drive, there are some important factors to keep in mind:
- The flash portion wears out over time – Like all flash storage, the flash portion has a limited lifespan and number of write cycles.
- Lack of visibility into tiers – Users have no visibility of where files reside between the flash and HDD portions.
- Tiering not customizable – The automated tiering process cannot be customized or configured by users.
- Drives not individually usable – The flash and HDD portions cannot be accessed individually, only as the combined logic unit.
- File system dependence – Fusion Drives require Apple’s AFPS file system, limiting compatibility with older macOS versions.
For advanced usage cases desiring more control, having the OS and apps on a dedicated SSD while using larger HDDs for data storage may be preferable to a Fusion Drive. But for more basic everyday usage blending speed and capacity, Fusion Drives present an appealing option.
Conclusion
Flash storage like SSDs offer faster pure solid-state storage, while Fusion Drives leverage both flash memory and HDD capacities to create a hybrid solution. Fusion Drives utilize the flash portion to cache frequently used data and optimize performance, while less accessed data resides on the larger HDD.
While Fusion Drives blend the best of both flash speed and HDD capacity, they also come with some limitations around flash wear, visibility, and customization. For most mainstream users a Fusion Drive can provide a good balance of speed and capacity. But power users may still prefer dedicated SSD and HDD storage devices for more granular control.