bench: invalid read measurement w direct io

[jamesmarkchan]

fedora on a nuc is not reporting realistic read values as this is a legacy intel NUC BLKNUC7i5DNH which should be a PCIe 3 interface limited to 32 Gbps (~3,940 MB/s) Gen3 x4 NVMe SSD.

This drive uses SATA III interface internally so is restricted to 6Gbps SATA standard.

Per samsung specification the specs on this drive are:

Sequential Read Speed: Up to 550 MB/s.
Sequential Write Speed: Up to 520 MB/s.
Random Read Speed (4KB, QD32): Up to 97,000 IOPS.
Random Write Speed (4KB, QD32): Up to 88,000 IOPS.

Samsung_SSD_860_EVO_Data_Sheet_Rev1.pdf

need to understand how to accurately perform read benchmark with direct io or disable direct io in this environment.

this is performance with non direct AND root (so drop catch should be enabled) io so both readings are not looking valid.

[jamesmarkchan]

this is with write sync enabled. write looks within the bounds, of course low but read is off the charts per the hw specs.