How to get the current Write Speed



Hi All,

I want to know how to find the current Write speed of my Drive after I issue WRITE MMC command.
I have got a list of all supported Write and Read speeds using GET PERFORMANCE command.

Please help me find the Current Write Speed.

Thanks in advance!


Current write speed is available in bytes 28-29 of the CD/DVD Capabilities and Mechanical Status page.


Thanks for replying.
But if I am not wrong this is legacy now. I mean deprecated. Is that true?


Hi Sohail K,

T10 has been calling 2A a legacy structure for years but I find
it continues to be in use. The MtFuji Group makes no mention of it being legacy. Maybe T10 feels it competes with their profiles/features scheme.
I don’t know but I find in the real world page 2A is more reliable. I still use
both but I can get some really bogus returns from Get Config/features.
That’s not T10’s fault of course. It’s the manufacturers.

I can call the Real-Time Streaming feature and check the MP2A bit,
find it at 0 and then call 2A and get perfectly good returns. Try it.

The field mentioned by Spath is the only value I know that gives you
"the actual data rate that the logical unit is currently using." quote MtFuji.
The Kbytes per sec in byte 28 is the unit’s write speed after initializing
with disc in the tray. That’s the speed it’s going to write at unless you
change it.

I call Get Performance and/or Read TOC/ATIP (CD only) to get
recommended device and disc write speeds and check it against 2A/
‘Current Write Speed Selected’. If they match or are in the ball park
I leave the speed setting alone. Unless you are trying to force the speed up
a notch over recommended ? Otherwise I think you can use & trust 2A.




Sorry …
>>The Kbytes per sec in byte 28 is the unit’s write speed …
should be byte 29
byte 28 bit 0 & 1 is the CLV rotational control value



Thanks for the detailed explaination. I have used 2A and it works fine for me.

Can you tell me what is the difference between 2A Byte#28-29 and GET PERFORMANCE Performance Data response?


Probably both are the drive manufacturer’s recommended write speed for the disc in the drive.

To get/set write speeds for CD -R/W only drives to use 2A (bytes 28-29) & Set CD Speed, for DVD +/- R/W and CD/DVD Combo drives to use GetPerformance/Write Performance/End Speed & Set Streaming.

There are reported to be DVD drives that will not return a valid 2A. My old Plextor CD only writer (401240A) returns good Get Performance values. Andy Polyakov, author of growisofs, who knows a lot more than me says Set CD Speed is obsolete and to always use Set Streaming to change the speed. A value of FFFFh will set it to “optimum” where the drive’s bios decides the best write speed.

You do not send these commands during a write loop to check the speed.

For more details on 2A download the SCSI-3/MMC-3 (T10/1363-D, November 12, 2001) from the T10 website.




Thanks a lot. This helps me understand better.

Have a nice day!

I have already used 2A and it works fine for me. Thanks for help