SanDisk Extreme PRO and Crucial X6 4TB Portable SSDs Review: Contrasting High-Capacity Storage Optionsby Ganesh T S on August 18, 2021 9:30 AM EST
Synthetic Benchmarks - ATTO and CrystalDiskMark
Benchmarks such as ATTO and CrystalDiskMark help provide a quick look at the performance of the direct-attached storage device. The results translate to the instantaneous performance numbers that consumers can expect for specific workloads, but do not account for changes in behavior when the unit is subject to long-term conditioning and/or thermal throttling. Yet another use of these synthetic benchmarks is the ability to gather information regarding support for specific storage device features that affect performance.
Western Digital claims claims read and write speeds of around 2 GBps for the SanDisk Extreme PRO Portable SSD v2, while Crucial claims speeds of 800 MBps for the X6. Both of these are backed up by the ATTO benchmarks provided below. ATTO benchmarking is restricted to a single configuration in terms of queue depth, and is only representative of a small sub-set of real-world workloads. It does allow the visualization of change in transfer rates as the I/O size changes, with optimal performance being reached around 512 KB for a queue depth of 4 in the SanDisk model, and around 128KB for the X6.
The ATTO read numbers for the X6 were a bit off, despite repeated retries. As the rest of the benchmarks show, the X6 is only able to reach advertised numbers for real-world workloads.
CrystalDiskMark uses four different access traces for reads and writes over a configurable region size. Two of the traces are sequential accesses, while two are 4K random accesses. Internally, CrystalDiskMark uses the Microsoft DiskSpd storage testing tool. The 'Seq128K Q32T1' sequential traces use 128K block size with a queue depth of 32 from a single thread, while the '4K Q32T16' one does random 4K accesses with the same queue configuration, but from multiple threads. The 'Seq1M' traces use a 1MiB block size. The plain 'Rnd4K' one uses only a single queue and single thread . Comparing the '4K Q32T16' and '4K Q1T1' numbers can quickly tell us whether the storage device supports NCQ (native command queuing) / UASP (USB-attached SCSI protocol). If the numbers for the two access traces are in the same ballpark, NCQ / UASP is not supported. This assumes that the host port / drivers on the PC support UASP.
The ability of the SanDisk Extreme PRO to support the NCQ / UASP features was never in question. The X6 with its native flash controller is the more interesting product in this case, and we see that it does support the features essential for SSD-like performance.