OK, here's what the manual page for
hdparam sas:
Code:
-t Perform timings of device reads for benchmark and comparison purposes. For
meaningful results, this operation should be repeated 2-3 times on an other‐
wise 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 measure‐
ment is an indication of how fast the drive can sustain sequential data
reads under Linux, without any filesystem overhead. To ensure accurate mea‐
surements, the buffer cache is flushed during the processing of -t using the
BLKFLSBUF ioctl.
and
Code:
-T Perform timings of cache reads for benchmark and comparison purposes. For
meaningful results, this operation should be repeated 2-3 times on an other‐
wise inactive system (no other active processes) with at least a couple of
megabytes of free memory. This displays the speed of reading directly from
the Linux buffer cache without disk access. This measurement is essentially
an indication of the throughput of the processor, cache, and memory of the
system under test.
And you can take a look at
http://linux.about.com/od/lsa_guide/a/gdelsa44.htm for some additional discussion.
Hope this helps some.