The performance of the storage bridges / drives in various real-world access traces as well as synthetic workloads was brought out in the preceding sections. We also looked at the performance consistency for these cases. Power users may also be interested in performance consistency under worst-case conditions, as well as drive power consumption. The latter is also important when used with battery powered devices such as notebooks and smartphones. Pricing is also an important aspect. We analyze each of these in detail below.
Worst-Case Performance Consistency
Flash-based storage devices tend to slow down in unpredictable ways when subject to a large number of small-sized random writes. Many benchmarks use that scheme to pre-condition devices prior to the actual testing in order to get a worst-case representative number. Fortunately, such workloads are uncommon for direct-attached storage devices, where workloads are largely sequential in nature. Use of SLC caching as well as firmware caps to prevent overheating may cause drop in write speeds when a flash-based DAS device is subject to sustained sequential writes.
Our Sequential Writes Performance Consistency Test configures the device as a raw physical disk (after deleting configured volumes). A fio workload is set up to write sequential data to the raw drive with a block size of 128K and iodepth of 32 to cover 90% of the drive capacity. The internal temperature is recorded at either end of the workload, while the instantaneous write data rate and cumulative total write data amount are recorded at 1-second intervals.
| Sequential Writes to 90% Capacity - Performance Consistency | |
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Similar to its 2TB cousin, the 4TB T7 Shield doesn't have a SLC cache cliff. Other PSSDs have notable performance loss after the initial write burst. The SanDisk Extreme PRO's loss is from a higher level and its steady state is still much better than the theoretical limit of 1GBps-class PSSDs. Thermal performance is excellent and similar to that of the 2TB version of the T7 Shield.
Power Consumption
Bus-powered devices can configure themselves to operate within the power delivery constraints of the host port. While Thunderbolt ports are guaranteed to supply up to 15W for client devices, USB 2.0 ports are guaranteed to deliver only 4.5W (900mA @ 5V). In this context, it is interesting to have a fine-grained look at the power consumption profile of the various external drives. Using the Plugable USBC-TKEY, the bus power consumption of the drives was tracked while processing the CrystalDiskMark workloads (separated by 5s intervals). The graphs below plot the instantaneous bus power consumption against time, while singling out the maximum and minimum power consumption numbers.
| CrystalDiskMark Workloads - Power Consumption | |
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Despite the additional flash packages, the power consumption profile of the 4TB version is very similar to that of the 2TB version. Peak power consumption is around 4W, and there is a deep-sleep mode after 15 or so minutes of inactivity where the PSSD draws just 160 mW from the host.
Concluding Remarks
The Samsung Portable SSD T7 Shield 4TB version is available for purchase today. The official launch MSRP is $430, but we already saw the PSSD for sale at $410. This pricing is completely untenable, given the price of competing PSSDs. The SanDisk Extreme PRO v2 comes with a USB 3.2 Gen 2x2 20 Gbps interface, has a much better performance profile across all considered workloads, and the 4TB version is currently available for $360. On the flip side, it is only IP55-rated, and the power consumption numbers are a bit on the higher side.
If the PSSD is priced between $250 and $300 (closer to the Crucial X6), one can look past the disappointing random access performance and the DRAM-less nature that affects performance for workloads of power users (including application launches and read/write of small files). Even at the higher end of that pricing spectrum, one can say that the PSSD would deliver excellent value for typical direct-attached storage workloads. The IP65 rating and low power consumption, coupled with the hardware encryption capabilities (controllable via the Samsung Portable SSD Software) are important value additions. Samsung's upcoming release of their Magician software is also expected to introduce cloning of internal SSDs to PSSDs such as the T7 Shield.
In terms of scope for improvement, we believe Samsung should offer DRAM-equipped PSSDs in a slightly premium line - those could deliver better performance for non-DAS workloads (and PSSDs are starting to get treated on par with internal SSDs by power users already). They could also explore supplying a single Type-C to Type-C cable along with an attached Type-C to Type-A adapter.
In conclusion, while the performance and feature set of the Portable SSD T7 Shield are acceptable for an entry-level PSSD, the pricing appears to be one meant for a high-end one. The market deserves a wider range of PSSD offerings from Samsung with varied performance levels and commensurate pricing.
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