CDROM read ahead questions!!
 

Hi all,

I wanted to know how to change the CDROM read ahead values?
This is required for my latest work on a live cd based distro!!!!

I have very vague idea of what a read ahead means..
Is it something like a seek buffer that prefetches data before the head accesses that particular track ?,or something like that?
Secondly is there a way to turn it off completely?

Thanks

I assume your trying to get your CDROM to run faster (data wise)?

Well the problem is not necessarily the speed the CDROM/DVD can read data. If it is, then its hardware bound to the speed of your CD/DVD drive, its internal memory, and probably its internal firmware operation.
All you can do CD/DVD wise is ensure your got the device alone on a IDE || SCSI || SATA channel, where no other device will interfere with its operation.

What is usually the problem with GUI style Live-CD's is the amount of available memory (RAM) your system has [especially true for X], the style of interface (IDE is much slower than SATA II), your video/graphics card and its memory capability, and your CPU speed/capability.

For a quick speed up, put a lot more CPU memory in - so that the complete live data is in-memory rather than having to go read off and re-read from the CD/DVD drive. However - If you concerned only with the speed of LOADING the initial Live-CD to the point where it is operational for you the user, you will need to increase the speed and capability of ALL the hardware as outlined in the previous paragraph.

In this case making the best usage of the CPU memory wont come into picture,
reason being, ive developed a method of booting the live cd from RAM directly.
So now the OS has no dependency on the CD at all.
But this is not good enough for me ;)
The technique ive followed is to copy the compressed FS to the RAM and use it as the default image to boot from!
But the catch here is that,when the copy is being done,there is nothing else that is happening , all the CPU time is just dedicated to this process...
And its this cp that is taking a large chunk of my boot time.

So i wanted to know if there is a way to boost the read ahead ,so that we can increase the prefetch from the current 4 pages?

There is no tuning available to increase the read-ahead cache size which is something relatively recent (nv77).

Have a look at this bug report that details the mechanism and files involved:

http://bugs.opensolaris.org/bugdatab...bug_id=6588256