"Failed to Read Sectors" - Please satisfy my curiosity

[AlbertEinstein]

 

I am a computer nerd and am asking this question out of pure curiosity since either answer makes no difference from the big picture perspective when imaging a movie DVD. ImgBurn reports what appear to be ranges of failed sectors in 64K chunks(32 * 2048 = 65536 bytes). But then follows up with different numbers of individual unreadable sectors beneath. In the first failed range of 32 sectors we see that it explicitly states 3 sectors as unreadable.

 

W 20:52:56 Failed to Read Sectors 318208 - 318239 - Reason: L-EC Uncorrectable Error

W 20:53:06 Failed to Read Sector 318208 - Reason: L-EC Uncorrectable Error

W 20:53:06 Sector 318208 maps to File: \VIDEO_TS\VTS_01_1.VOB

W 20:53:15 Failed to Read Sector 318209 - Reason: L-EC Uncorrectable Error

W 20:53:15 Sector 318209 maps to File: \VIDEO_TS\VTS_01_1.VOB

W 20:53:24 Failed to Read Sector 318210 - Reason: L-EC Uncorrectable Error

W 20:53:24 Sector 318210 maps to File: \VIDEO_TS\VTS_01_1.VOB

 

In this second chunk of my log file we see that ImgBurn reported only 2 specific unreadable sectors:

 

Failed to Read Sectors 409328 - 409359 - Reason: L-EC Uncorrectable Error

W 20:55:19 Failed to Read Sector 409344 - Reason: L-EC Uncorrectable Error

W 20:55:19 Sector 409344 maps to File: \VIDEO_TS\VTS_01_1.VOB

W 20:55:28 Failed to Read Sector 409345 - Reason: L-EC Uncorrectable Error

W 20:55:28 Sector 409345 maps to File: \VIDEO_TS\VTS_01_1.VOB

 

So my simple question is, given this example, is there 64 unreadable sectors or only 5 unreadable sectors? Does it dump sectors in chunks of 32 or at the individual sector level? The latter would be good to hear in spite of almost no practical difference, just because.

 

**EDIT**: My follow-up question relates to the one above. Is the 32 sector range that ImgBurn "appears" to work with a hard-coded preset in the ImgBurn software? Can it be configured by the user? Or is this much more determined by your optical hardware device? Is the 32 sector range completely arbitrary or has it been determined as the optimal setting for DVD optical drives? The number of sectors read at a time is called a 'block'?

Edited October 25, 2015 by AlbertEinstein

[LIGHTNING UK!]

You can configure it to read 64kb (32 sectors) or 32kb (16 sectors) at a time. Asking a drive to read 1 sector at a time results in very slow performance, so it reads 16 or 32 and drops down to single sector when the drive reports an error. It then returns to 16 or 32 after a while.

 

Only the errors during single sector reads are actual errors that'll cause data to be missing from your image file.

 

For DVD, the ECC block size is 16 sectors. For BD it's 32. So reading in chunks of 16 or 32 is normal.