Crucial X8 in the test: The one with the large cache writes


Current ultrabooks and HEDT systems for AMD's Threadripper v3 or Intel's Core i9 have a suitable connection: We are talking about USB 3.2 Gen2 with a transmission speed of 10 GBit / s. There are few suitable external SSDs on the market, so far we have only tested the Adata SE800 and a DIY version. With the X8, Crucial enriches the segment with another model and follows a clever approach.

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The X8 is based on a 128 x 93 x 24 mm housing, which is noticeably larger than that of the Adata SE800. Crucial includes a USB-C cable and an adapter to USB-A. Inside the external SSD there are two boards instead of one because Crucial, unlike Adata, relies on existing hardware instead of designing its own design for the X8: There is an M.2-2280 SSD in the metal body, to which an adapter board is connected with bridge chip from NVMe on USB.

A look at the 2280 board shows that Crucial has installed an SM2263EN controller from Silicon Motion, which is connected to the DRAM and flash memory of the parent company Micron. The NAND is the current QLC memory, i.e. 64 layers of 4-bit cells. We know this hardware combination from the Crucial P1, but for the Crucial X8 the manufacturer has designed the firmware somewhat differently.

Crucial X8 (Image: Marc Sauter /

QLC memory has 16 charge states, which is why write processes take a comparatively long time. For this reason, an SLC buffer is used, data is written with one bit instead of four bits and the information is saved in idle pauses from the write cache in free QLC cells. With the Crucial P1 with 1 TB, the SLC buffer holds at least 12 GB to dynamic 150 GB depending on the fill level, with the Crucial X8, however, the manufacturer has designed it more generously with up to 180 GB when empty. The SSD was preformatted via ExFAT, so it is under common (operating) systems ready for immediate use.

We measure a read and a write rate of 1,010 MByte / s, which is a bit higher than the Adata SE800 with 985 MByte / s. To classify: Theoretically, USB 3.2 Gen creates up to 1.25 GB / s. In practice, the ASM2362 bridge chip from Asmedia does not limit performance because it supports two PCIe Gen3 lanes, but the USB interface minus overhead. To exhaust the SLC buffer, we have to copy several large Steam game folders to the Crucial X8, then the write rate drops from a good 600 MB / s to 90 MB / s.

Crucial sells the X8 for 135 euros (500 GB) and for 185 euros (1 TB), which makes it a bit more expensive than the Adata SE800, which has been available for some time. The excellent performance and above all the large write buffer make the Crucial X8 recommendable if it doesn't have to be the most compact external USB 3.2 Gen2 SSD on the market.

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