SATA II RAID 0 not reaching 3.0 Gbps

Man-wai Chang ToDie (33.6k) wrote:
HDTach free version.

It really does?
>>
>Yes, it calls it the "Burst Speed".
>
>
Do you happen to know why HDTune doesn't report 3Gbps burst speed?
HDTach really reported burst speed of 3Gbps
>

HDtach and HDtune both report read burst speed, which should be the speed
*measured* when copying data from the HD's cache into the PC's main
memory. For the measured burst speed to be equal to the SATA link
peak speed (150/300 MB/s for SATA-I/II), every component in the chain
between the HD's cache and the PC's main memory must be at least as
fast as the SATA link, including the data mover engine between the
HD's cache and the SATA, and the data mover engine(s) between the SATA
link and the PC's main memory.

HDtach and HDtune do not always agree on read burst speed. For example,
the WD740 on this P4 with a SATA-I link is reported by HDtach as 119.4 MB/s
read burst, while HDtune shows 101.9 MB/s. Since HDtach's reported data
agrees with Storage Review and with WDC's (vendor) site, you can easily
guess whether I believe HDtach or HDtune.
--
Cheers, Bob

There are also other factors that will effect trying to acheive the theoretical maximum.

Things like disk fragmentation, drive free space, bus utilisation, drive configuration, driver efficiency and other factors will directly or indirectly effect these figures.

Another important factor is the SATA II 3.0Gbps transfer speed is the theoretical maximum speed of the interface which is control information and actual data. this means the data transfer rate will always be something less when you take out the control data overhead.