Packet and cdrom interface differences
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. 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. Best regards, DS.
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.
participants (2)
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Dominik Smogór
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Phillip Susi