Sizing Backup, Bootable and Storage partitions on an External Disk

Question

I have iMac G5, 2 GB RAM, 1 TB HD with one partition currently holding about 140 GB, and a TB external disk. I want to use the external disk for three purposes: Bootable Partition, Time Machine Backup, Miscellaneous Storage.
Apple advises matching the capacity of the Time Machine backup to that of the volume being backed up. My inclination is to limit the Backup volume to 500 GB, see how that works out and re-evaluate as HD use increases.
Q1. As I understand, the bootable partition would be, at the minimum, a duplicate of all OS X (Leopard in the case of G5s) system and application software.
Q2. Should it also include 3rd party apps? (yes?)
Q3. Should it be a pristine installation that is independently kept up to date with all upgrades, but essentially unused unless an emergency arises? (yes?) Or is it okay to somehow sync it with my HD content? (this could copy a problem to just where you don't want it to be?)
Since I will be using Time Machine to backup my HD, it does not seem that all the data files (e.g. iTunes Library) need to be included in the bootable partition.
Q4. What are the correct choices for what goes into the bootable partition, including 3rd party apps and data?
Q5. What process should be used for updating this software? Independent, parallel updates? (yes?)
Q6. Are there any files that should be duplicated in this partition; for example, keychains are something you need - or would you get these from Time Machine too?
Q7. Since the Time Machine backup resides on the same disk, it is possible to restore needed files from there. When Time Machine restores the system, does it put everything into the boot partition? (yes?)
Q8. If so, since Disk Utility allows dynamic re-partitioning, I could use a limited space for the bootable partition and then re-allocate more space to it later if I wanted to run a fully restored version of the system off the external disk? (yes?)
Q9. Does it make sense to separate the Miscellaneous Storage into a separate partition? (yes?) Or should should I use just one partition to hold the bootable stuff and the miscellaneous stuff? (no?)

Answer 1

Mr. Cat wrote:
Mostly agreeing with Kappy here, but a few additions.
Apple advises matching the capacity of the Time Machine backup to that of the volume being backed up. My inclination is to limit the Backup volume to 500 GB, see how that works out and re-evaluate as HD use increases.
That should be plenty, depending on how the 140 GB will grow. Our "rule of thumb" is, TM needs 2-3 times the space of the data it's backing-up. See #1 in the Frequently Asked Questions *User Tip,* also at the top of this forum.
Q1. As I understand, the bootable partition would be, at the minimum, a duplicate of all OS X (Leopard in the case of G5s) system and application software.
That depends on what you're trying to do, and how much space you have, but usually a bootable clone contains everything. Thus it's partition should be a minimum of 120% of the data on (or anticipated to be on) your internal HD.
Think for a moment about why you want two separate, independent backups. The safest route is to have them on separate disks, so you're protected against either disk failing (and they all do, sooner or later). For that reason, consider getting another disk for the clone. If you get a portable one, you can take it to a secure off-site location, so you're also protected against fire, flood, theft, and direct lightning strike on your power lines. Some folks get a pair of them; use one for a week or so, then take it off-site and swap with the other one.
The other reason to have two backups is to protect you against a problem with one app or drive; thus if your TM backups somehow get corrupted, you still have the clone, and vice-versa.
In both cases, your best bet is to let both apps back up nearly everything. Sometimes there's a good reason to omit some things; see #11 in the FAQ Tip for more detail. Also, if you're running Windoze via virtualization software, you likely do not want to back it up with Time Machine. See #9 in the FAQ Tip.
Q5. What process should be used for updating this software? Independent, parallel updates? (yes?)
I use CarbonCopyCloner, in addition to full Time Machine backups; SuperDuper is similar. Both are reliable. CCC is donationware, SD has a free version, but you'll need the paid one (about $30) to do automatic scheduling and updates (vs. a full replacement). Both are easily found via Google.
Q7. Since the Time Machine backup resides on the same disk, it is possible to restore needed files from there. When Time Machine restores the system, does it put everything into the boot partition? (yes?)
You select the destination disk/partition.
Q8. If so, since Disk Utility allows dynamic re-partitioning, I could use a limited space for the bootable partition and then re-allocate more space to it later if I wanted to run a fully restored version of the system off the external disk? (yes?)
Yes, but be careful. You can only resize a partition by dragging the bottom in the diagram up or down; you can't move the top. Thus to expand a partition, you have to delete the one below it.
Q9. Does it make sense to separate the Miscellaneous Storage into a separate partition? (yes?) Or should should I use just one partition to hold the bootable stuff and the miscellaneous stuff? (no?)
They should each be separate. See #3 in the FAQ about the TM partition; and you'll also want the clone to be on it's own partition.
Since you have a lot of room on the external, I'd recommend putting the TM partition first, and the most-easily replaced partition(s) last.
You might want to use the Restore option of Disk Utility to make a copy of your Install disc in a small partition on the external (towards the end). It's much faster and easier to boot from that instead of trying to find your Install disc, when you need to. I'd also recommend making a duplicate of that disk and keeping it in a secure off-site location.