Re: Packet and cdrom interface differences

Dominik Smogór wrote:
> Hello everyone.
> What is the actual difference between characteristics of packet writing
> device and plain writable ide /dev/dvd for dvd+-rw media.
> 
> They both seem to serve the same purpose but I observed vast differences.
> 

When using the dvd device directly, you are relying on the drive's 
firmware to perform the read-modify-write cycle required to update an 
individual sector.  The firmware support for this is often poor.  With 
the pktcdvd driver, writes are held until a full packet can be written, 
or a timeout happens, and then the read-modify-write is performed.  This 
tends to result in fewer read-modify-write cycles, and thus, better 
throughput.

> 1. even if writing operation on udf formated media is completed in both
> cases, the plain dvd seems to have very inefficient elevation strategy
> virtually killing the drive with excessive seeks. This happens both in case
> of many small files as well as a single large one. The pkt device is much
> smoother and in turn faster in both cases.
> 
> 2. Some Udf disks written through the pkt interface are erratically read
> through plain device in rw mode (which look to be a more file system
> interpretation problem that sector level io). They are hovewer correctly
> read by dvd device in ro mode.
> 
> Another question is how to best tune mkudffs parameters in case of both
> dvd+rw and cdrw to minimize seeks and maximize writing speed?
> The pkt driver reports fixed 64k packets for my drive. The usage pattern is
> incremental only medium file writes, with occasional overwrites so the
> fragementation is not a concern form me.

It is best to use pktcdvd to access it.  Other than that, there isn't 
much you can do.