How much partition for an alternate start up disk?

[av8rdave]

I have Mac OS X 10.5.6 and want to make an alternate start up disk on my 250 GB external (USB) hard drive.

Does anyone have any idea how large a partition I should make for it?

Thanks!

[struggle4progress]

1. How will you use the partitions? Are you planning, for example, to

use one piece to clone your internal hard-drive and the other for Time Machine, for example? Are you going to put a copy of the install disk on one piece and a clone of your internal hard-drive on the other?

[av8rdave]

2. I was planning on one partition for an alternate startup disk

and the other for time machine backups.

[struggle4progress]

3. Since I'm not expert, take everything I say with shaker of salt:

(1) You don't need a humongous amount of disk space for the operating system: I installed enough of Leopard on a 16GB USB flashdrive to be able to get my system up (IIRC, I didn't install all the available fonts and languages). But it was incredibly slow: perhaps some of the problem is the USB, and firewire might do better

(2) Required memory probably depends on what you intend to do once you boot from the partition. If you're planning to use this as an emergency way to continue working if your internal disk dies, you need room for whatever critical programs you have on your internal drive. Most apps will produce a fair number of temporary files as well, and some of these will be stored to disk, so you'll need some space for that

(3a) If you plan to use the boot-up partition for recovering some TM data in the event of an internal drive failure, then you need to allocate some space for that also. But my guess would be that's not a particularly good idea -- it may not work well: you'd be asking a single head both to read from one partition and write to another, and I'd expect that to be very slow if there's a lot of data to copy
(3b)For my own machine, I decided to set aside one disk for TM and another as a bootable recent clone of my primary disk -- then, if I have to rewrite or replace my primary disk, I've got a fairly recent copy from which I can approximately restore, after which I'd hope to use TM to complete the restoration
(3c)If I were going to try doing what I think you want to do, I think I'd want an external drive of size at least ((size of my primary drive) + 1.5*(maximize size I expect to use on my primary drive in the next few years)), and I would set one partition to be the (physical) size of my primary drive and give the rest to a partition for TM: then I would clone my primary drive to the first partition, after which I would set up TM to use the drive
(3d) Here's another idea, but I don't know whether it's good or not: partition your external drive so that one piece has enough room for your original install disk: http://www.macosxhints.com/article.php?story=20071025021604930

[av8rdave]

4. Thanks...I'm thinking option 3d

I just want to be able to boot up and have a shot at recovery if my OS or hard drive run into trouble. I figure if I can get things restored, then I could use my TM data to replace most of my files (hopefully).

If I wanted to clone my entire hard drive to a partition, I would definitely need a larger external drive (probably not a bad idea anyway - they aren't that expensive anymore).

A related question (if you happen to know): Once I have a partition set up, is it simply a matter of copying my start up disk (that came with the computer) to set up an alternate boot, or is there something more involved (remember, I'm new to Mac)?

Thanks for the info!

[struggle4progress]

5. Since I haven't tried most of this myself, don't take my comments too seriously

For a full system recovery, I can find instructions that use the installation disk
http://docs.info.apple.com/article.html?path=Mac/10.5/en/15638.html
http://www.macobserver.com/article/2008/01/28.15.shtml

I can easily find instructions of the following sort of the web, but it's always unclear to me whether the people advocating it have actually verified that one can successfully restore in this way
http://www.thegraphicmac.com/create-bootable-time-machine-backup-drive
http://www.macfixit.com/article.php?story=20071101112529955

[struggle4progress]

6. I tried a variant of this: partitioned a driv into 3 volumes, first a wee big bigger than the

install disk (according to Get Info), second a wee big bigger than my start-up disk, and third whatever space was left

My TM is on a second external drive

Cloned the install disk to the first volume. Shut down. Rebooted into the install disk volume. Then restored (via TM) my whole system to the second volume. The 49GB or so on my startup drive took about 1.5 hrs to restore on the second volume of the partitioned drive

Comments: (1) There's a nuisance: the install disc folder pops up on every reboot (2) There's an obvious security issue here, since the install disk gives lots of access to the machine

[struggle4progress]

7. Here's another variant I tried. I partitioned an external drive into two pieces:

one part is about 2.5 times the size of the disk to back-up, and will be used for TM
the rest is what remains (but larger than the size of the disk to back-up)

I ran TM to backup the main disk to one volume of the partitioned disk

I cloned the OS X installation disk to an 8GB flash drive

I then restarted with the flashdrive inserted, selecting the OS X installation volume on the flashdrive as the boot disk, and jumped the hoops to get the TM restore going

<edit> 25GB or so was restored in less than an hour. The machine rebooted to the restored volume on the external drive. There was no network access to the notebook during the restoration, although it was connected physically to my network, but access exists after the reboot

Why would I want to do this? In an emergency I should be able to boot from the restoration on the disk: if my notebook internal drive died, I could restore everything and get access to the files I need, using only a partitioned external drive containing my TM data, together with a pre-prepared flashdrive. So this is a relatively portable recovery mechanism

Potential disadvantages: the flashdrive install disk gives complete access to the machine, so this solution requires some special care to maintain security. Moreover, this is probably works the external harddrive pretty thoroughly, since the read-write head has to wander back and forth from the region storing the TM data to the region where the system restoration will be written

One other remark: the restored external volume has the same volume name as the original internal volume, so it's absolutely necessary to change the name of the restored external volume