Finnix Forums » General Discussion

1. rfinnie
   Administrator

   Submitted by SourceForge user nazo
   
   Well, first of all, the outer edge of the CD is read faster than the inner (I'd been told this for a while, but, more recently I've benchmarked on clean discs when testing media quality, and in every case the speed starts around 20x or so and moves almost exactly linearly up to 48x on a good 120mm disc.) I say this because you mention that you optimize the filesystem by placing most immediately needed startup data in the inner loop. I don't much care about the bootup speed myself, but, if you want to absolutely maximize it as much as possible, it might be a good idea to look at seeing if there is a way to move as much as possible towards the end of the disc (in fact, dummy empty data, eg dd if=/dev/zero, is a trick I often use to force the most important stuff of mine to the very edge of the disc for maximum speed.)
   
   I don't know how much difference that will make though. Especially since you still have the most important thing -- placing the data close together so that the laser isn't forced to skip back and forth trying to read it. In fact, this whole thread may be pointless if you have to have a certain amount of data at the beginning of the disc no matter what (I'm thinking of, for example, things like kernel and initrd.) It may still end up faster just because the laser doesn't have to move much. If you've already tried this or know that it won't work, then I'm sorry, but, if either isn't true, it may be worthwhile to try a few tests and see if you can make it even better for those who most appreciate the speed differences (and, hey, better competition, right?)
   
   Also, you specify that your ultimate goal is to have a live distro which fits on a mini-CD of 185MiB. As far as I know it isn't even possible to find or buy those anymore. They have all been replaced with 210MiB discs (I even have 210MiB mini-CDRWs) much like the old 650MiB CDRs have been replaced with the 700MiB CDRs. I know it doesn't make MUCH difference and none at all now since Finnix is still around the general area of 100MiB. I'm just worried that should you someday start to reach that limit that you may end up sacrificing some functionality to keep it fitting on a 185MiB disc when supporting the 210MiB discs would probably not really hurt anyone (and anyone still holding onto 185MiB discs probably should take advantage of the extra storage newer discs offer considering that the mini-CD/DVDs are limited to something like 30% of their full sized counterparts.) To me it seems that if you can find a rewritable version of such a disc then it's pretty well the final stamp on the death of the old kind since rewritables are more expensive and less common. I understand the idea of supporting the old kinds, but, only if the old kinds even are common enough to be worth supporting. To me it seems like it is better to not sacrifice content for support of completely depreciated media.
   
   Not that it matters if you never even get close to 185 MiB, and so far with keeping things as efficient as they are, they don't come close to a question of 185 MiB versus 210MiB.
   
   Clearly these things are unimportant and even if they were important, they are more long term thoughts than short term, so just something to think about.
   
   http://sourceforge.net/tracker/index.php?func=detail&aid=1472542&group_id=3892&atid=103892

   Posted Wed, 21 Jun 2006 15:43:27 -0700

2. rfinnie
   Administrator

   Yep... you are right that it is slower toward the inner ring of a CD, but that don't affect performance too much on a livecd. Instead, latency introduced by drive seeks are the real performance killers, and the script that determines order for the CD is designed to try to get startup files as close to each other as possibe.
   
   Also, 185MB CDs exist, as well as 210MB. This is the same issue as the old 650MB CDs vs today's 700MB. The CD diameter is the same, just with more usable data. However, while 650MB CDR media is virtually dead, there is still enough 185MB CDRs being sold that I consider it a good size goal.

   Posted Wed, 28 Jun 2006 18:22:52 -0700