Performance

Out of the box, the Crucial X8 comes formatted with the exFAT filesystem, which ensures maximum compatibility for Mac users, so I was curious whether reformatting to NTFS is worth it; the results are listed below.

I also tested the Crucial X8 against a few competing solutions, most notably the ADATA SE800, which is is a brand-new external drive with support for 10 Gb/s USB 3.2 Gen 2, too. I also tested the Samsung 850 Pro SATA SSD using a cheap $7 USB-to-SATA adapter. Last but not least, the performance of the Samsung 850 Pro and Crucial P1 on their native interfaces, connected directly to the host PC, is reported.

An additional data point (red bar) shows performance of the Crucial X8 when connected to a "traditional" USB 3.0 port, one which does not support the fast 10 Gbps interface speed, but ticks at 5 Gbps only.

Random IO

Random read/write performance matters if you copy a lot of small files or use the drive as storage for games/applications that are directly started off the drive.

Performance is solid, almost as good as the Samsung 850 Pro on the SATA 6 Gbps interface. Surprisingly, exFAT actually does a tiny bit better here than NTFS, but the differences are not worth picking one filesystem type over the other.

Sequential IO

Sequential performance is relevant when you copy large files, for example videos. Performance here is clearly limited by the maximum USB bandwidth of 10 Gbps (or 1 GB/s).

While we do see the drive reach the promised 1 GB/s transfer rates, that only happens when you copy multiple data streams, which is highly unlikely. Usually, you run just a single file copy operation, which is exactly why our comparison charts report speeds at realistic queue depths.

Sustained Write Speeds

Sequential write speeds start out very high at around 700 MB/s while the pseudo-SLC cache gets filled up. Once it is exhausted (after around 180 GB of writes), the drive has to write to its QLC flash directly, dropping speeds to only 100 MB/s, which is really slow. However, you have to consider that it's highly unlikely any consumer will write that much data in one go. What's great is that the pSLC buffer is big—on many TLC drives, it's in the order of 4 GB to 16 GB. Crucial opted for a much larger one capable of soaking up all but the biggest write bursts. Once the write activity stops and the drive is idle, the pSLC cache gets flushed to QLC in the background and full write performance is restored.