From Fedora Project Wiki
- robatino - CD sizes are measured in MiB (so the size of a "700 MB" CD is actually closer to 700 MiB - see http://en.wikipedia.org/wiki/CD-ROM#Capacity), but DVDs are measured in GB (so a "4.7 GB" DVD is almost exactly 4,700,000,000 bytes - see http://en.wikipedia.org/wiki/DVD#Capacity). I'm not sure about the minimum size - is it 2 MiB, or 2 MB?
- robatino - I've been told there's no specific minimum size, so it doesn't really matter.
- jlaska - I think this test has a larger focus on ensuring that the ISO's are not larger than the media for which they are intended (e.g. CD or DVD). However, a minimum size was also added so that we weren't shipping media with no packages. As is sometimes the case during the compose process, a disc6.iso can be produced which contains no packages. This is rare, but also something the disk size check was validating. Hope this helps!
- robatino According to http://en.wikipedia.org/wiki/Binary_prefixes#Flash_drives, the advertised size of USB flash drives is in SI units.
- robatino For RC4, the exact size of F13-Beta-i686-Live-KDE.iso is 734003200 bytes. A zero-byte file of this size can be created with the command
dd if=/dev/zero of=dummy-file bs=2048 count=358400
Running the prescribed test on it shows a size of 701M, even though its exact size is 700 MiB = 700*1024^2 bytes. Are the KDE live images still supposed to be CD-sized, and if so, does this image pass the test, or not?
- robatino Informative post from the test list on exactly how much can fit on a CD: http://lists.fedoraproject.org/pipermail/test/2010-April/089943.html
In particular, it appears that an exactly 700 MiB image will fit.
- robatino The ISO size should be the same as what the ISO header says it should be - the product of the Logical block size and Volume size listed by "isoinfo -d -i file.iso". I noticed that in the Nouveau test day, one of the Live ISOs was bigger than what the header indicated. I've never seen this with install images, though. This would be easy to test since it doesn't require downloading the full ISO, just the beginning of it. Should this be added as an additional test?
- robatino I notice that the spins use a target size of 703 MiB instead of 700 MiB for CDs. I'm not sure whether it's worth exceeding the advertised size to gain an extra 3 meg, but http://en.wikipedia.org/wiki/CD-ROM#Capacity suggests it should be okay. If we want, we could switch to 737148928 bytes (703 MiB = 703*2^20 bytes) instead. However, check out http://lists.fedoraproject.org/pipermail/test/2010-April/089943.html for possible risk involved.
700 MiB vs 703.125 MiB
Bruno asked why 703.126 MiB wasn't used instead of 700 MiB for the single CD-ROM image size. Andre noted that, according to http://lists.fedoraproject.org/pipermail/test/2010-April/089943.html, 703 MiB might not be safe.
My feeling is unless you're really, really sure that it is, it's not worth exceeding the advertised size of 700 MiB (with the understanding that's what "700 MB" actually means) to gain at most an extra 3 meg.