From hdparm man page:
-t Perform timings of device reads for benchmark and comparison purposes. For meaningful results, this operation should be repeated 2-3 times on an otherwise inactive system (no other active processes) with at least a couple of megabytes of free memory. This displays the speed of reading through the buffer cache to the disk without any prior caching of data. This measurement is an indication of how fast the drive can sustain sequential data reads under Linux, without any filesystem overhead. To ensure accurate measurements, the buffer cache is flushed during the processing of -t using the BLKFLSBUF ioctl.
What is the "buffer cache"?
- The hardware cache/buffer in hard drives and in some ssd drives?
- The caching that the OS does using RAM, ie not using the cache on the harddrive. I think this is called page caching.
Maybe it's obvious for most, but it is not for me :)