Whole-Drive Fill

This test starts with a freshly-erased drive and fills it with 128kB sequential writes at queue depth 32, recording the write speed for each 1GB segment. This test is not representative of any ordinary client/consumer usage pattern, but it does allow us to observe transitions in the drive's behavior as it fills up. This can allow us to estimate the size of any SLC write cache, and get a sense for how much performance remains on the rare occasions where real-world usage keeps writing data after filling the cache.

The SLC write cache in the 1TB SK hynix Gold P31 runs out after just over 100GB of writes. After the SLC cache fills up, the Gold P31's sequential write performance becomes highly variable, ranging from about 1.4 to 2.3 GB/s with little change in character across the entire TLC filling phase. There are no obvious patterns of periodic garbage collection cycles visible at this scale.

Sustained 128kB Sequential Write (Power Efficiency)
Average Throughput for last 16 GB Overall Average Throughput

Despite the variability, the P31's long-term sustained write performance is excellent. It averages out to the best overall write throughput we've measured from a 1TB TLC drive, and in all that variation the performance never drops down to a disappointing level.

Working Set Size

Most mainstream SSDs have enough DRAM to store the entire mapping table that translates logical block addresses into physical flash memory addresses. DRAMless drives only have small buffers to cache a portion of this mapping information. Some NVMe SSDs support the Host Memory Buffer feature and can borrow a piece of the host system's DRAM for this cache rather needing lots of on-controller memory.

When accessing a logical block whose mapping is not cached, the drive needs to read the mapping from the full table stored on the flash memory before it can read the user data stored at that logical block. This adds extra latency to read operations and in the worst case may double random read latency.

We can see the effects of the size of any mapping buffer by performing random reads from different sized portions of the drive. When performing random reads from a small slice of the drive, we expect the mappings to all fit in the cache, and when performing random reads from the entire drive, we expect mostly cache misses.

When performing this test on mainstream drives with a full-sized DRAM cache, we expect performance to be generally constant regardless of the working set size, or for performance to drop only slightly as the working set size increases.

As expected for a drive with a full size DRAM buffer, the P31's random read latency is unaffected by spatial locality: reading across the whole drive is just as fast as reading from a narrow range. And the only other TLC drives that can match this read latency are the two Toshiba/Kioxia SSDs with 96L BiCS4 TLC NAND, but they can't maintain this performance across the entire test.

SK hynix Gold P31 1TB Review AnandTech Storage Bench
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  • TheinsanegamerN - Thursday, August 27, 2020 - link

    Looks like a fantastic laptop drive.

    Now, if only we could get some nice 4800/4850U laptops to go with it.
    Reply
  • Walkeer - Friday, August 28, 2020 - link

    there is one: schenker via 15 pro / tuxedo: https://www.tuxedocomputers.com/en/Linux-Hardware/... Reply
  • TheinsanegamerN - Monday, August 31, 2020 - link

    that's a 4800h, not a 4800u. The 4800U has 8 GPU slices, the 4850U has 9. The 4800h has the same GPu performance as a 4700u, as both have 7 slices.

    It's confusing. The analog for H series would be a 4900h. I saw that laptop earlier and it would be perfect if it had a 4900h and lpddr4x, but alas it does not.
    Reply
  • Luminar - Thursday, August 27, 2020 - link

    There are barely any 2242 drives on the market. Wish there were more. Reply
  • vladx - Thursday, August 27, 2020 - link

    Very few motherboards including for laptops are limited to 2242 size. The only real use case would be tablets, sadly that market is in a steep decline. Reply
  • Luminar - Thursday, August 27, 2020 - link

    Many laptops use the 2242 form factor. All Thinkpads do, at least for the secondary drive slot.

    Finding a 2242 was difficult so I had to Dremel down a 2280 drive to the 2242 form factor.
    Reply
  • TheinsanegamerN - Friday, August 28, 2020 - link

    Uh huh. So you cut a 2280 drive down to size and got a nice light show? Because you cant just dremel off a flash NAND chip and expect the drive to work properly.... Reply
  • Luminar - Friday, August 28, 2020 - link

    Of course you can Dremel off a good amount of the WD SN500/520 series of drives. As AnandTech wrote in their review, the electronics are contained in the first 30mm of the PCB for all SN500 drives, whether they be 2280, 2242, or 2230. Reply
  • TheinsanegamerN - Monday, August 31, 2020 - link

    OK, fair enough theSN500syou can do that. I've never seen a M.2 drive like that befor,e they've always had chips along the entire 80mm length. Reply
  • cfbcfb - Sunday, August 30, 2020 - link

    Yeah, you have to fold it over and use some duct tape on it.

    A computer without at least one piece of duct tape is just not cutting it.
    Reply

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