User:Gordon/Optical Drive Testing Script - Revision history

Gordon: /* Software dependencies */

2009-12-27T21:49:12Z

Software dependencies

Gordon: /* Software dependencies */

2009-12-27T21:47:55Z

Software dependencies

Gordon at 21:34, 27 December 2009

2009-12-27T21:34:02Z

Gordon: /* Meeting testing needs */

2009-12-27T21:04:06Z

Meeting testing needs

Gordon: /* Initializing discs for testing */

2009-12-27T20:54:49Z

Initializing discs for testing

Gordon: /* Software interface specification */

2009-12-20T01:19:42Z

Software interface specification

Gordon: /* Software interface specification */

2009-12-20T01:18:47Z

Software interface specification

Gordon at 01:10, 20 December 2009

2009-12-20T01:10:45Z

Gordon: /* Media longevity and recycling */

2009-12-18T23:43:09Z

Media longevity and recycling

Gordon at 23:41, 18 December 2009

2009-12-18T23:41:52Z

@@ Line 57: / Line 57: @@
 * The script, if written by me, will be written in Python (whatever version is installed by default in Ubuntu 9.10)
 * The script will depend on [http://www.cdrkit.org/ cdrkit], including (but not limited to) 'wodim' and 'genisoimage'.
 For semi-current information, see [[/scratchpad|the dev scratchpad]] for this project.

@@ Line 57: / Line 57: @@
 * The script, if written by me, will be written in Python (whatever version is installed by default in Ubuntu 9.10)
 * The script will depend on [http://www.cdrkit.org/ cdrkit], including (but not limited to) 'wodim' and 'genisoimage'.
 ==Software interface specification==

@@ Line 1: / Line 1: @@
 <div style="float: right;">
 __TOC__
-<big>'''[[/current status|current status]] :: [[/time log|time log]] :: [http://bitbucket.org/gmfreegeek/lazers/ source code]'''</big>
+<big>'''[[/current status|status]] :: [[/time log|time log]] :: [http://bitbucket.org/gmfreegeek/lazers/ code]<br>
 </div>
 ==Why automate optical drive testing?==

@@ Line 28: / Line 28: @@
 # The drive's mechanical function can be tested with a CD-ROM read test which reads and verifies data from both the central and peripheral surfaces of a disc.  If the drive cannot spin properly, the test will fail.  If the laser sled is sticky, it may fail to read the outside or inside edge of a disc.  I propose to use pre-burned CD-ROMs with multiple sessions containing files full of random data for which a hash is known.  The basic read test would read the innermost and outermost session on the disc, verify the data it gets back using the hash, and time the test so as to reject drives which are returning valid data only after many retries.
 # The above test also implicitly tests the CD read laser/pickup.
-# To test the CD write laser, a data file would be written to a CD-RW and then read back and verified.  This would be done in sessions.  I believe there is ~20MB overhead per session, so write 15MB data + 20MB overhead = 20 sessions per CD-RW disc before the disc must be blanked.
+# To test the CD write laser, a data file would be written to a CD-RW and then read back and verified.  This would be done in sessions.  "Lead-in and lead-out of the first session occupy 28 MB that is reduced to 13 MB for all following sessions. Twenty sessions therefore have 275 MB of overhead, and only 378 MB is available for user information."[http://www.mscience.com/faq67.html] Therefore, a maximum of about 18.9MB of data should be burned per session on a 20-session disc.
 # To test the DVD read laser/pickup, a similar test as done for the CD function would be done with a pre-burned DVD-ROM.
-# To test the DVD write laser, a similar (but larger) data file as for the CD-RW test would be written to a DVD+RW and then read back and verified. As it turns out, writing multisession DVD-RW discs is highly problematic at best,[http://club.myce.com/f34/dvd-rw-multisession-questions-306321/] and DVD+RW is far more likely to work for multisession burning in a wide variety of drives.  Thus I am reversing my earlier position on using DVD-RW media, as it would have to be quick-blanked for every test; this disadvantage plus its other disadvantages is enough to tip the scales in favor of DVD+RW in my opinion.
+# To test the DVD write laser, a similar (but larger) data file as for the CD-RW test would be written to a DVD+RW and then read back and verified. DVD+R session overhead is about 4MB per session.[http://answers.google.com/answers/threadview/id/299164.html] Minus 80MB for session overhead, there is about 4402MB of usable capacity on the disc, meaning a maximum of about 220MB of data should be burned per session on a 20-session disc. As it turns out, writing multisession DVD-RW discs is highly problematic at best,[http://club.myce.com/f34/dvd-rw-multisession-questions-306321/] and DVD+RW is far more likely to work for multisession burning in a wide variety of drives.  Thus I am reversing my earlier position on using DVD-RW media, as it would have to be quick-blanked for every test; this disadvantage plus its other disadvantages is enough to tip the scales in favor of DVD+RW in my opinion.
 Eventually, rewritable media will either wear out or become scratched and dirty and need to be replaced.  How to detect this and whether the user can be automatically instructed to discard old media is an open question.  It can probably be solved either by obtaining a unique ID from the discs themselves and keeping a log in a database, or writing an ID to the discs as part of their initialization.

@@ Line 68: / Line 68: @@
 <code>lazers init cd-r /dev/sr0</code><br>
-<code>lazers init dvd-r /dev/sr0</code><br>
+<code>lazers init dvd+r /dev/sr0</code><br>
 <code>lazers init cd-rw /dev/sr0</code><br>
 <code>lazers init dvd+rw /dev/sr0</code><br>

← Older revision		Revision as of 01:18, 20 December 2009
Line 58:		Line 58:

	==Software interface specification==		==Software interface specification==
		+	I've chosen to name the command line program 'lazers'.
		+
		+	Usage:
		+
		+	<code>lazers [command] [options] [device]</code>
		+
		+	===Initializing discs for testing===
		+	Initializes discs for use as test media.
		+
		+	<code>lazers init cd-r /dev/sr0</code>
		+	<code>lazers init dvd-r /dev/sr0</code>
		+	<code>lazers init cd-rw /dev/sr0</code>
		+	<code>lazers init dvd+rw /dev/sr0</code>
		+
		+	===Testing a drive===
		+	(Requires initialized media of every type that will be used to test the drive.)
		+
		+	<code>lazers test /dev/sr0</code>

	==Media longevity and recycling==		==Media longevity and recycling==

@@ Line 53: / Line 53: @@
 * Creating a .deb package with proper dependencies, so that it could be added to Free Geek repos etc, would be great!
-==Dependencies==
+==Software dependencies==
 * The script, if written by me, will be written in Python (whatever version is installed by default in Ubuntu 9.10)
 * The script will depend on [http://www.cdrkit.org/ cdrkit], including (but not limited to) 'wodim' and 'genisoimage'.
 ==Media longevity and recycling==

@@ Line 58: / Line 58: @@
 ==Media longevity and recycling==
-* CD-RW and DVD-RW has a maximum rewrite lifetime of about 1,000 writes, though in practice this is probably much lower, and the discs will become scratched and dirty before they are rewritten 1000 times.
+* CD-RW and DVD+RW has a maximum rewrite lifetime of about 1,000 writes, though in practice this is probably much lower, and the discs will become scratched and dirty before they are rewritten 1000 times.
 * With a strategy of writing 20 test sessions a disc before a quick blank, a disc could be blanked and re-used 10 times in order to test 200 optical drives. This would rewrite the entire surface of the disc 10 times.  I suspect discarding discs after this point may be a good rule of thumb as discs will inevitably become physically damaged over time.
 * CD-RW and DVD+RW media consist of a writable layer containing (among other elements and compounds) antimony and tellurium, which are toxic.  Discs should be appropriately recycled and not smashed or broken.

@@ Line 59: / Line 59: @@
 ==Media longevity and recycling==
 * CD-RW and DVD-RW has a maximum rewrite lifetime of about 1,000 writes, though in practice this is probably much lower, and the discs will become scratched and dirty before they are rewritten 1000 times.
-* With a strategy of writing 20 test sessions a disc before a quick blank, a disc could be blanked and re-used 20 times in order to test 400 optical drives. This would rewrite the entire surface of the disc 20 times.  I suspect discarding discs after this point may be a good rule of thumb as discs will inevitably become physically damaged.
+* With a strategy of writing 20 test sessions a disc before a quick blank, a disc could be blanked and re-used 10 times in order to test 200 optical drives. This would rewrite the entire surface of the disc 10 times.  I suspect discarding discs after this point may be a good rule of thumb as discs will inevitably become physically damaged over time.
-* CD-RW and DVD-RW media consist of a writable layer containing (among other elements and compounds) antimony and tellurium, which are toxic.  Discs should be appropriately recycled and not smashed or broken.
+* CD-RW and DVD+RW media consist of a writable layer containing (among other elements and compounds) antimony and tellurium, which are toxic.  Discs should be appropriately recycled and not smashed or broken.
-* CD-R and DVD-R media consist of a metal reflective layer and a writable layer of organic dyes of various types.  The dyes are more stable (particularly in premium discs such as Taiyo Yuden CD-Rs) than the writable layer in rewritable discs, so the longevity of prerecorded test CD-Rs and DVD-Rs will likely be determined by physical damage from abrasion, heat, UV and humidity.
+* CD-R and DVD+R media consist of a metal reflective layer and a writable layer of organic dyes of various types.  The dyes are more stable (particularly in premium discs such as Taiyo Yuden CD-Rs) than the writable layer in rewritable discs, so the longevity of prerecorded test CD-Rs and DVD+Rs will likely be determined by physical damage from abrasion, heat, UV and humidity.
-* I don't know about the toxicity of CD-R and DVD-R dyes.  The discs should be properly recycled and not broken or smashed.
+* I don't know about the toxicity of CD-R and DVD+R dyes.  The discs should be properly recycled and not broken or smashed.
 * I recommend Taiyo Yuden CD-Rs based on their proven dye stability.