I recently started reviewing live-cd options, primarily a custom gentoo live cd, or in my case live dvd. This was prompted because of a hard drive death taking out my install.
I was considering using a live-cd while I await a new hard drive. But I began thinking... Why use a hard drive at all? I only used it for the OS, all my important files are stored on my server.

I am aware of some security benefits of a livedvd, for instance a hacker could not modify the OS filesystem should they get it, the most they might be able to do is restart or shutdown the system, no biggie. As well hard drive failures are not a problem. And DVD drives basic ones, are less than the top of the line hard drives (thought he same cost as the one that died).

I am also aware of some downside: updates require new discs to be burned, this is a continuing cost as apposed tot he hd's one time cost.

But I have the following questions:

What is the speed difference in access times and transfer rates in sata 7200rpm drives vs. 16x dvd-rom reading from a dvd burned at 16x? As well as flat theoretical data rates what are we talking when it comes to contiguous files, for instance I am assuming that files are written to an iso file in a sensible structure and order.

Would one of these options be noticably faster than the other?

I am an enthusiast, I do not simply install and use, I configure compile install, change everything.

I use gentoo from a stage 1 install on 2 servers, a laptop, and a desktop (See list in my signature) Then I also manage a gentoo stage 1 install on the server where I work.

I know that for me (compiling new programs to play with every day) a livecd would not be practical on my desktop system. But I think it might be beneficial on at least one of my servers.

So I am not looking for opinions on you should or should not do this, I do not care what you think I should do, I am interested in facts and speed information so I can make my own descisions in my own situations.

IIRC you get a bit less than 10 MB/s transfer on a 8x DVD, compared to ~150 MB/s on a sata disk. The difference is easily seen if you put a ide disk on the same cable as a dvd or cd-drive because the bus uses the transfer rate of the slowest disk on the cable. If you want you can do some simple tests on this.
Kanotix and Knoppix use unionfs as a overlay filesystem so you can install progs to a live cd. You will of course have to save them on a hd so you won't lose them on a reboot.
Personally I think the biggest annoyance of running a livecd is the noise from the drive, not data rate.

First off, where can I get a hard drive that actually goes 150mb/s? that would be sweet, for me sata to sata transfers on my new 250gb sata western digital drives from one to another tops at around 26mb/s.

10mb/s is definately slower, but that is just tranfer, what about finding files? or initial access to the files?, for instance I ls /some/dir it takes a moment to build the list if there are a LOT of files/directories in the dir, same goes for loading diaolgues in program windows. What is the comparison?

Noise does not bother me, it is so hot at night I use a huge fan near my bed that makes more noise than my systems. and outside my always open window is interstate 89 in a resort community, noise is not an issue because it gets drowned out fast.

Sorry, the 150 was the internal data transfer rate. Last time I ran partimage from a livecd copying data from hd to hd, both ata, I believe the transfer rate was ~25 MB/s being about same as yours. Even so, for your system you could simply clock the dvd by copying a directory to a dvd and comparing to accessing the same on a hd.
A typical access time mentioned in dvd specs is 150 ms while hd's go at 8-12 ms.

thank you, this has been most informative and helpful. :-D

Well I know it wasn't terribly helpful but the thing is that you can get all the hard facts about transfer rates on your specific hardware and it won't tell you much anything. The easiest way to see how your drives, I/O busses etc work together is to clock it yourself.

A bit OT but,since you like livecd's for yourself...how about kanotix...it has unionfs which allows you to use apt-get and install what you like...even update your system.
Together with "toram" and "home=scan"(scans at boot for persistent home directory)
You can,if you have one,stick a usb thumbdrive and use as your persistant home directory.
With enough memory you can even do a full apt-get update apt-get dist-upgrade provideing its not a real old livecd disk.
There should be a new Kanotix live cd out in the next week or so...the reason I mention this is because updateing the existing livecd would be somewhere between 500 pakages.you would need 4gigs of ram..lol.
I have used this method during my move on one box...I have 2gigs ram and loaded my livecd toram and have a 1gig thumb drive usb2 I used for persistent home directory.I successfully updated the 2005.4 livecd with over 400pakages.

Mepis knoppix all use unionfs and toram option.....not sure about gentoo as it has been some time since I used gentoo livecd.

good luck.


edit;
(more info not relative)

I also just now before writeing this installed kanotix CPX-Mini to a 512mb usb thumbdrive...it uses fluxbox,unionfs and persistant home directory....quite nice if you ask me.
http://www.informatik.hu-berlin.de/~bading/cpx-mini/

Theres also another iso for usb thumbdrives of kanotix that uses xfce....benix;
http://debian.tu-bs.de/project/benix/