An exclusive controller with extra NAND
Tisdale may be a new face on the desktop, but it's been around for a while. This controller chip first appeared in Intel's DC S3700 server drive in late 2012. Intel's last SSD controller was competitive for multiple generations, though, so Tisdale's age shouldn't be an issue. Think of it as mature rather than old.
On the surface, the Tisdale controller looks pretty conventional. It has eight parallel NAND channels, and it can address up to eight dies per channel. A 6Gbps Serial ATA interface provides the connection to the host. 256-bit AES encryption support? Check.
Well, sort of. Enterprise implementations of the controller support full-disk encryption, but the 730 Series does not. Intel has once again trimmed a business-friendly feature from an enthusiast-oriented product. This propensity for arbitrary product segmentation is maddening, but outside of laptop use, few enthusiasts are likely to miss AES-256 support. Intel says the 730 Series' high clock speeds make the drive unsuitable for most notebooks, anyway.
Like its enterprise counterparts, the 730 Series pairs its flash controller with a gig of RAM. These speedy DDR3-1600 chips never hold user data. Instead, they're used for context and indirection tables.
User storage is handled by the flash memory, which is spread between physical 16 packages on the 480GB model Intel provided us for testing. Each of the underlying NAND dies stores two bits per cell and has 64Gb (16GB) of total capacity.
SSDs in the 480-512GB range typically employ 512GB of flash memory, so on a drive like this, one would expect to find 32 dies. However, the 730 Series 480GB has 33 dies for a total of 528GB. The 240GB model also has an extra flash chip, for a total of 272GB rather than the usual 256GB.
Despite the surplus flash, the 730 Series doesn't offer any additional storage to the user. Windows reports the same 447GB of available space as with the other 480GB SSDs we've tested. The extra NAND is part of the drive's overprovisioned spare area, which is reserved exclusively for the controller. This spare NAND provides a pool of empty flash pages that can be used as a landing pad for incoming writes, a working area for drive management routines, and a source of viable flash to replace bad blocks.
The spare area is also tapped by a parity-based redundancy scheme designed to preserve user data after larger-scale flash failures. Some desktop SSDs employ similar RAID-like protection, but they don't include additional flash, which limits the amount of overprovisioned area available to other tasks.
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At first, the 730 Series will be limited to 240GB and 480GB configurations. Intel says there are no barriers to producing higher-capacity models and that customer demand will determine whether any are made. The controller should be able to support up to 1TB of flash using the same dies as the existing models.
Note that the 240GB variant has much lower write speed ratings than its 480GB sibling. The sequential rating is off by 42%, and random writes trail by 24%. The random read rating is 3% lower, as well. These specifications suggest the 730 Series requires a minimum of 32 NAND dies for optimal performance. The 240GB model simply doesn't have enough flash to harness all of the controller's internal parallelism.
The 240GB model also has a lower endurance rating than its big brother. The smaller drive is rated for 50GB of writes per day for five years, while the 480GB unit is supposed to be good for 70GB/day over the same period. Intel's other desktop drives are rated for only 20GB of writes per day for three or five years, depending on the model, so the 730 Series represents a big step up.
The per-day ratings add up to 91TB and 128TB of host writes, respectively. That sounds like a lot, and in the context of a desktop drive, it definitely is. Intel's 335 Series 240GB drive is rated for only 22TB of total writes. If you've been following our ongoing SSD Endurance Experiment, though, you'll know our findings show that desktop drives can absorb vastly more use than their specs tend to claim. Most users will be hard pressed to take advantage of any additional endurance the 730 Series offers in real-world use.
Same old toolbox
The best way to monitor the health of the 730 Series' flash is with Intel's SSD Toolbox software. This utility provides two health indicators on the main interface, and the accompanying SMART attributes provide even more information about the state of the drive.
Users can access the SMART data with the Intel utility or via third-party monitoring tools. In addition to counting the number of sectors that have been reallocated due to flash failures, the SMART attributes track several different error types. They also display the total volume of host reads and writes.
Most of these attributes display data about the SSD's life as a whole. The 730 Series also has three attributes related to a timed workload function that should provide details on shorter periods of activity. We're still waiting to hear back from Intel on how to reset the workload log, but the related attributes track elapsed time, media wear, and the ratio of read and write requests.
Since the SSD Toolbox has so much SMART data at its fingertips, I'd like to see more details displayed on the main screen. Otherwise, the utility is great. It has just about everything one might need, including a firmware updater, a secure erase tool, drive diagnostics, and a system optimization feature. Slick software isn't strictly necessary for an SSD, but it's a nice perk that isn't available with all drives.
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