New to Mac - do I need to create a start-up disc?

Question

Hi
I've recently switched over to an iMac from PC - I've worked with macs but I didn't have to deal with back-ups myself (they were all networked)
I have an external HDD which uses Time Machine to back-up - I did hope to use that as back-up and keep a stash of stock photos (large file!) on there too but I've heard that it's not a good idea to do that (even if I partitioned the drive)
My main issue is that I've heard that the back-ups cannot be used as a 'start-up' disc in case something happens to the iMac - so can someone let me know how I should go about doing this? (I didn't get any discs with the iMac so what do I do if something does happen?)
and while I'm asking questions... do you think I should get another external HDD? one to use for photo storage etc (I work professionally with Photography so they are large files) and then use the other for time-machine?
can you use a smaller sized HDD for time-machine? (the external drive I have now is 500GB -
Model Name: iMac
Model Identifier: iMac8,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.8 GHz
Memory: 4 GB
Hard Drive 320GB

Answer 1

I've moved over from a PC to a MBP since May, and have dealt with similar backup issues concerning backups of software projects (also large files) daily. So I can share my thoughts and experience here.
1) I would keep the photo file originals on a separate external USB HDD (not the Time Machine backup) with Read-Only attribute. When I copy files from my Mac to an external disk drive, I think it automatically takes on an archive attribute (read-only). With Leapord 10.5, I think that drive can even be in NTFS format (as used by Windows XP & Vista).
Since HDD eventually fails, I would, over time, back up these high resolution photos on Dual density (8GB) DVDs.
Because it'll probably take too many DVDs to back up al the photos, an easier option is to purchase an external backup drive systems that automatically back up a copy of your data on its own separate physical HDD package inside the same box. At the minimum, the box would actually contain two identical size HDD, but you get to use only one. The second drive is for the automatic backup. These boxes are called RAIDs, and a decent one will notify you when it detects a disk error on any one of the two drives so you can preventively replace the faulty drive to give your data full protection. The best I've seen cost $800 list for a TeraByte of protected disk storage. This box actually uses multiple data redundancy schemes to give you flexibility in buying HDDs as your need grows, but you do need to start with at least two drives for data protection. See...
http://www.drobo.com/WheretoBuy/Index.html
A review of its abilities and limitations was published on ZDNet..
http://blogs.zdnet.com/Ou/?p=508
The author of the review called himself his first review harsh, and I agree since the limitations was due to physics and user selection of disk drives that were installed, no design.
2) For any photo files that I am manipulating daily, I would keep them on my Mac so that Time Machine so that every revision I make is backed up.
As far as whether you need to create a start-up disk, I believe the answer is no. From Apples own online documentation, you can recovering your Mac installation from Time Machine. I understand that if you allow Time Machines to back up up everything (default setting), the procedure to full system recovery is:
1) Reformat the boot disk and restore MacOS X from the CDs that came with the computer.
2) Connect the external Time Machine backup drive, bring up Time Machine and restore. You can find the details by searching the Time Machine discussions. I saw some users even tried the procedure out for real.
I've consider using one of the many backup software to back up a full disk image of my Mac, so I re-install my Mac with that disk image. The problem with this is it's a duplicating backup scheme: twice the amount of work and cost. And when the mac crashes, which one backup do I use?