Playing with CD-RWs on FreeBSD


I didn’t realise until just now that Jörg Schilling, the principle maintainer of cdrtools, died last year. I’ve been writing about his software for ages, yet never got around to sending him a thank you. I consider this a wakeup call to appreciate people who make my life better.

But I digress. I’ve been throwing away tons of old crap, some of which were ancient CD-Rs which I imaged and saved as ISOs. My plan is to use a few CD-RWs to boot and ferry data to my retrocomputers and for data centre trips, and only burn stuff as I need it. It saves space and money, and reduces the amount of one-time use plastic waste I’m generating.

The FreeBSD Handbook already includes excellent CD-burning instructions, so instead I’m going to explore how rewriteable media works. As a quick refresher, you find out which device ID your burner is, then provide it an ISO:

# cdrecord -scanbus
==> ...
==> scsibus7:
==> 7,0,0 700) 'PLDS' 'DVD-RW DU8A6SH' 'DL62' Removable CD-ROM
==> ...
# cdrecord dev=7,0,0 image.iso

My first attempt to burn an ISO onto an old CD-RW failed:

cdrecord: Cannot get next writable address for 'invisible' track.
cdrecord: This means that we are checking recorded media.
cdrecord: This media cannot be written in streaming mode anymore.
cdrecord: If you like to write to 'preformatted' RW media, try to blank the media first.
cdrecord: Disk capacity is unknown.

The hint was on line four. This disc was already full of data, so I have to blank it first. I hadn’t had coffee all morning, so my mind was doing this already.

For those who don’t remember the joys of optical media, there are many ways to blank, wipe, clear, or reformat a disc prior to writing new data. The quickest and most common is fast, which only overwrites the table of contents (TOC) and program memory area (PMA) at the start of the disc, indicating the rest of the disc can be overwritten, not unlike a quick format of a hard drive. My anecdotal experience is you can do this a few times before the error rate and failed burns become more common.

# cdrecord dev=$DEVICE blank=fast

It’s probably overkill, but I’ve got into the habit of always blanking all the disc each time. It takes the equivalent of writing an entire disc worth of data, because that’s what it’s doing! But the end result is a nice, clean disc for new data.

# cdrecord dev=$DEVICE blank=all

Now we can record our ISO image again. I’m always interested to see the capabilities of drives I use, even if at best I understand half the features here. This is a simple SATA slimline unit in my primary FreeBSD tower:

Copyright (C) 1995-2019 Joerg Schilling
scsidev: '7,0,0'
scsibus: 7 target: 0 lun: 0
Using libscg version 'schily-0.9'.
Device type    : Removable CD-ROM
Version        : 0
Response Format: 2
Capabilities   :
Vendor_info    : 'PLDS    '
Identifikation : 'DVD-RW DU8A6SH  '
Revision       : 'DL62'
Device seems to be: Generic mmc2 DVD-R/DVD-RW/DVD-RAM.
Using generic SCSI-3/mmc   CD-R/CD-RW driver (mmc_cdr).
Supported modes: TAO PACKET SAO SAO/R96P SAO/R96R RAW/R16 RAW/R96P RAW/R96R

It’s worth mentioning as well that CD-RWs do typically take longer to burn that a CD-R, even discounting the time taken to blank them. It’s more than an acceptable compromise for me, but don’t be surprised if the drive reports 4 for the drive speed. I did briefly have a CD burner and CD-RW media as a kid that worked at 8×, but both those are long gone.

This was a fun experiment! Now I have a reliable way to generate these disc images with a few CD-RWs.

Author bio and support


Ruben Schade is a technical writer and IaaS engineer in Sydney, Australia who refers to himself in the third person in bios. Wait, not BIOS… my brain should be EFI by now.

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