Miscellaneous Aspects and Concluding Remarks

The performance consistency for real-world applications was looked at in the previous section. We recently added a test to determine the effectiveness of the thermal solution for sustained workloads. After deleting the SSD volume, a fio workload was 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, instantaneous write data rate, and total amount of data written in total till that point of time were recorded.

Sequential Write to 90% of Disk Capacity - Performance Consistency

The Seagate Fast SSD seems to have a 67C cut-off before thermal throttling kicks in. After that, the writes go down to around 100 MBps (with drops even going as low as 10 - 20 MBps). On the other hand, the SanDisk Extreme Portable SSD is a lot more consistent. The cut-off is 75C, and the drop after thermal throttling is to 50 MBps. However, the device tries to get back to peak write performance as often as possible, in constrat to the behavior of the Seagate Fast SSD.

The above exercise also allows us to determine the SLC cache size and/or the amount of data that can be written in one shot without a drop in the write data rate. The graphs below plot the transfer rate and the total data transfer amount from the start of the fio workload to the approximate timestamp at which the transfer rate shows a significant drop.

Sustained Writes - Characteristics

The Seagate Fast SSD shows two inflection points. The first one is quite early - after around 12GB of data transfer (as shown in the above graph). This is due to the shift from SLC cache to either directly writing data to the TLC region, or, a slowdown while transferring data from the cache to the TLC region. The SanDisk Extreme Portable SSD, on the other hand, shows a drop only after writing more than 250GB of data continuously. Even at that point, the drop is due to thermal throttling.

The SSDs being considered today are bus-powered, and it is given that the peak power consumption can't go beyond 4.5W to maintain compatibility with as wide a range of systems as possible. It is still relevant to take a fine-grained look at the power consumption profile. Using the Plugable USBC-TKEY, the bus power consumption for both SSDs was tracked while the CrystalDiskMark workloads were processed. The workloads were set up with an interval time of 30s.

Drive Power Consumption - CrystalDiskMark Workloads

The Seagate Fast SSD has peaks as high as 5W, while the SanDisk Extreme Portable peaks at 3.4W. The latter is obviously much more power efficient.

The performance of both SSDs is great and as advertised. The Seagate Fast SSD has higher short-term write transfer rates for real-world workloads, but, even a slightly sustained workload involving say, 15 - 20 GB, is likely to be handled in a more consistent manner by the SanDisk Extreme Portable SSD.

Moving on to the pricing aspect, we find Seagate at a disadvantage. The Fast SSD is priced at $280, but the SanDisk model is at $225, and the T5 1TB version is $250. The lack of verical integration might prevent Seagate from competing on price.

Price per GB

The Fast SSD does come with certain value-add features like dead-simple backup and sync software, and the Adobe Creative Cloud subscription. If the Fast SSD and the SanDisk Extreme Portable are within $5 - $10 of each other, the value additions could help tilt the choice in favor of the former. As it stands, the 1TB version of the SanDisk Extreme Portable is very attractively priced at $0.23 / GB. Compared to the Samsung T5, it boasts equivalent performance with a lower price and an IP55 rating. The choice of the SanDisk Extreme Portable is a no-brainer for power users. That said, the Seagate Fast SSD does come out on top in a lot of our typical DAS workloads that involve bursty writes. Some consumers might appreciate that aspect. However, at $280 (compared to SanDisk's $225), it appears to be a tough sell.

AnandTech DAS Suite and Performance Consistency


View All Comments

  • Roen - Friday, September 28, 2018 - link

    I wonder how Sandisk gets away with including non-compliant USB adapters for the sake of convenience.

    In the Type-C Specification, Section 2.2, with two sentences at the very end of the section.

    “USB Type-C receptacle to USB legacy adapters are explicitly not defined or allowed. Such adapters would allow many invalid and potentially unsafe cable connections to be constructed by users.”
  • Impulses - Tuesday, October 2, 2018 - link

    They get away because as a regulation body the USB-IF is kinda weak... I guess if SanDisk is using their logos they can fine/sue or call them out, I'll check out the retail box since I ordered one... But yeah that kinda adapter leaves the door open for people to do really stupid things and I doubt it was so much cheaper than just tossing in a Type A to C cable. Reply
  • NCM - Friday, September 28, 2018 - link

    I'm glad the tests addressed thermal considerations. I frequently use external drives to transfer large amounts of data. Sustained writes of a couple of hundred GB cause most SSDs to get pretty hot. I've been known to direct airflow from a compact USB powered fan on to the enclosure.

    It would be good to see enclosure manufacturers pay more attention to providing a decent heat transfer path from the NVRAM chips to the outside world. A simple pad with some thermal paste might work wonders.
  • descendency - Monday, October 1, 2018 - link

    On page 1,

    " It comes with two 18in. cables - a Type-C to Type-C, and a Type-A to Type-A one."

    The picture shows a Type-C to Type-A cable and a Type-C to Type-C.
  • Tams80 - Monday, October 1, 2018 - link

    Definitely Type-C to Type-C.

    Type-A to Type-A were a thing for a while (when USB 3.0 Micro B was the go to, but some companies decided (rightly) that that connector was stupid), so I can understand where the confusion may have occurred.
  • ecthroi - Sunday, October 7, 2018 - link

    the Amazon prices are both at 239.99 right now actually, in case anyone's just seeing this (like me). Reply
  • ravib123 - Sunday, November 11, 2018 - link


    Sandisk doesn’t honor their warranties and has a high failure rate. I had to give up on the warranty and buy intel/samsung/micron who do honor their warranties.

    Lessons learned.

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