Creating Volume on External Firewire HD

Hi,
Is there a step by step walkthrough on creating a new volume on an external HD? I have a lot of data on this disk so preferably I need to create this partition while leaving the data in-state on the external disk.
Thanks for any help.

You need a third party application like iPartition from Coriolis Systems to do this, erugalatha.
See http://www.coriolis-systems.com/iPartition.php
Make sure you check out the note on Leopard compatibility, too, though.
In some circumstances and for some purposes much the same effect can be obtained by creating a new disk image on the external drive, too.
Cheers
Rod

Similar Messages

I am trying to export my iPhotos to an external HDD. As soon as it gets to 200 photos, I get an error message that says unable to create volumes/freecom/my pictures. Can i remove this limit or increase it? I have nearly 17,000 pictures to export.

I am trying to export my iPhotos to an external HDD. As soon as it gets to 200 photos, I get an error message that says unable to create volumes/freecom/my pictures. Can i remove this limit or increase it? I have nearly 17,000 pictures to export.

1. What format is the external drive? It sounds like it's ina format that Macs can't write to. Is it a NAS or NTFS?
2. Easiest thing: just move your iPhoto Library to the external
Make sure the drive is formatted Mac OS Extended (Journaled)
1. Quit iPhoto
2. Copy the iPhoto Library from your Pictures Folder to the External Disk.
3. Hold down the option (or alt) key while launching iPhoto. From the resulting menu select 'Choose Library' and navigate to the new location. From that point on this will be the default location of your library.
4. Test the library and when you're sure all is well, trash the one on your internal HD to free up space.
Regards
TD

How do I back up my Boot Camp partition to external firewire drive?

I have a 15 GB Windows XP Boot Camp partition (FAT32). I want to back it up to a 120 GB external Firewire drive. (I know the backup won't be bootable). In OX X Disk Utility, I formatted the external drive as MS-DOS (FAT). I planned to do the backup using the Windows Backup utility.
However, when booted into WinXP, Windows will not recognize the external hard drive. I thought I might need to create a FAT32 partion of 32 GB or less on the external drive, but I apparently can't do this in OS X or Windows (since Windows doesn't recognize the drive).
Any suggestions on how to backup the Boot Camp partition will be appreciated. I'm mainly interested in preserving all programs and data. Ideally, a clone could be created that could be restored back to the original partition in bootable form, but from studying this and other forums, it dosn't seem to be easy to do this for a FAT32-formatted volume.

My goal was to create a bootable clone of my FAT32 Boot Camp partition, while at the same time increasing the size of the partition from 15 GB to 32 GB if possible. This is what I did:
1. As suggested in this thread, I used Disk Utility to create a disk image. I formatted it as MS-DOS (FAT), and made it 32 GB in size.
2. Used the Finder to copy all files from my 15 GB Windows XP partition to the new disk image.
The following steps were only to determine if the disk image is a viable backup:
3. Removed the internal hard drive with my original Win XP partition, and installed a new internal hard drive.
4. Used Boot Camp Assistant to create a 32 GB Boot Camp partition on the new internal drive.
5. Inserted my Win XP installation disk and started the Windows installation. Formatted the new partition as FAT32. (I used the long rather than the quick format method--not sure if this was necessary.)
6. Continued the Windows installation to the point of restarting the computer, at which time I used the Option key to boot back into OS X.
7. Used the Finder to copy all the files from the 32 GB disk image to the new Boot Camp partition. (This overwrote a few Windows files installed by the aborted Win XP installation.)
8. Restarted and used the Option key to select the new 32 GB Boot Camp Partition. Windows booted as usual with all files, programs, etc. from the original 15 GB partition. Windows did complain about "new hardware" and required a restart, but all appears normal.
This indicates that the disk image containing all the files from my original Boot Camp partition is a viable backup, and can be used to restore the partition if necessary. I'm not sure if formatting the disk image as MS-DOS (rather than Mac OS extended) was necessary, or not.

Sound Library Storage on External Firewire Hard Drive

I'm planning on using the 3-drive configuration for Logic 8 -- internal system drive (500 Gig) in bay #1 for Logic install -- second internal drive in bay #2 for audio recording -- and an external firewire drive for sound library storage.
I've got the *Apogee Ensemble* which doesn't like sharing the Mac Pro Firewire Bus. Given the significant demands made on the Mac Pro's firewire bus by Ensemble, the tech at Apogee suggested a PCI-e firewire card to create a second firewire bus for the external firewire drive (and any other firewire peripherals I have in mind).
*Question 1:* Does it matter whether this external drive is firewire 400 or 800? Will it make a noticeable difference?
I'm planning on partitioning this external firewire drive into three volumes as follows:
Volume 1 -- one-time back-up/clone of my current OS X Tiger hard drive contents.
Volume 2 -- ongoing cumulative back-up of new OS X Leopard install (we're waiting for 10.5.3)
Volume 3 -- sound library storage
*Question 2:* Will Logic or the Mac Pro have any problems streaming samples from a partitioned external firewire drive? (assuming neither volumes 1 or 2 are active while running a Logic session)

Well, I don't know about the unmounting, Kitesurfer, but I thought it was worth bringing up. I also thought it was possible to unmount one volume without the other disappearing, even though they're on the same disk. It may just be my particular external disk but I find that hard to believe. Also, I'm not sure if, because your CCC clone will be journaled, OS X interacts with it in any way. Someone else may be able to answer that.
I'm not a pro so I doubt my equipment will be of interest to you, but it's a 500GB Lacie mini hub. I also have a Lacie 250GB external, which has a clone of my sample library partition. Nobody recommends Lacie but I've had the 500GB for almost a year and the 250GB for over two years I think, and I've never had a problem (except maybe the unmounting issue).

Partitioning External Firewire HD Without Erasing

Hey Guys,
I've done some research regarding partitioning and it seems that I can not find a direct answer to this.
I would like to partition a 750 Gig external firewire Seagate hard drive into 2 partitions without erasing any of the current files. The is no OSX system on this hard drive. (Yes, backing up it always a good thing but I was curious if it can be done in the first place). I don't want to place another OSX system on the new partition either.
When using Disk Utility and clicking on the Partition tab, I clicked on the + button which gave me a second partition and I resized it.
*The top partition of the Volume Scheme reads:*
Storage 1
"To erase and partition the selected disk, choose the volume scheme, set options for each volume, and click Apply. To resize the volumes on the selected disk, drag the deviders between them and click Apply."
*This volume will NOT be erased.*
Size: 461.8 GB
Available Space: 227.6 GB
It is also formatted: Mac OS Extended (Journaled)
*The bottom partition of the Volume Scheme reads:*
Storage 1_2
"To erase and partition the selected disk, choose the volume scheme, set options for each volume, and click Apply. To resize the volumes on the selected disk, drag the deviders between them and click Apply."
*A new volume will be created*
Size: 234.4 GB
This will also be formatted: Mac OS Extended (Journaled)
The Hard Drive current info states:
Disk Description : Seagate
Connection Bus : FireWire
Connection Type : External
Connection ID : 906767668999250
Total Capacity : 698.6 GB (750,156,374,016 Bytes)
Write Status : Read/Write
S.M.A.R.T. Status : Not Supported
Partition Map Scheme : Apple Partition Map
Back to my original question.. I've read threads where hard drives were being erased, left, right and center using this Partitioning info. Can this drive be partitioned without erasing any of it and how well does it work?
Thank you..

it works exactly as disk utility says. all you had to do was press "apply" this will split your current drive in two with the data on the first partition remaining intact. enter "create new volumes" in disk utility help for details.

Installing Applications on external FireWire drive - a good idea?

Hello,
I'm planing in using a MacBook Pro with 128GB SSD. The idea is to install only essential stuff and store other things on an external FireWire 800-enabled HDD.
How big is the general difference in acces/transmission times compared to an internal generic HDD? And is the performace sufficient to even run applications from that external drive, should I run out of space on the SSD?
Will I spot a significant difference if I'm for example editing videos where all the files and the workspace are on that external drive while only Adobe Premiere is installed on the SSD?

Is the firewire drive new? Do you have any data on it? I am guessing the answers are Yes and No. If this is the case, the drive is probably formatted wrong for the Mac Pro. Depending on the manufacturer, the drive may be formated in FAT (for windows) or as Apple Partition Map. APM is for booting PowerPC (G3, G4, and G5 Macs). You have a Mac Pro and the drive needs to have a GUID partition. Drives without a GUID partition will not be recognized as valid targets in the installer.
If you follow the rest of this thread, and you have data on the firewire drive, it will be lost unless you back it up. That is your warning. To reformat the drive, do this:
1: Open /Applications/Utilities/Disk Utility
2: In the left column there will be a list of the drives and volumes available on the machine. The drive is listed first and the volume is indented beneath it. Select the Firewire drive, not its volume
3: On the right panel, select the Partition tab
4: Change the Volume Scheme setting from Current to One Partition
5: Give the new volume you are going to create a name
6: Press the Options button
7: There are three choices, GUID, APM, and MBR. Choose GUID since this is an Intel system. Press OK.
8: Press the Apply button - THIS WILL DELETE ALL DATA ON THE FIREWIRE DRIVE
Now reboot from the installation CD and perform the installation.
I will say however, that a drive with a boot OS on it is nice, but kind of useless. Isn't your data a little more important? Since you are not on Leopard, you might want to consider using ASR (the Restore tab in Disk Utility) to periodically clone your main volume to the backup volume. Then, not only do you have a bootable second drive but you also have all your data and personal settings. For extra credit go check out http://www.shirt-pocket.com/SuperDuper/SuperDuperDescription.html
Hope this helps

Booting os x from *partitioned* external firewire drive?

Hi all,
my internal hard disk (on a 12" powerbook G4 867 mhz running osx tiger 10.4.10) has started acting weird (many people are reporting failing hard drives, and I'm assuming mine is failing too), so I'm preparing for replacing it with a new hard drive.
I've backed up the drive to an external firewire drive (LaCie portable 80 GB firewire drive "Design by F.A. Porsche") using Carbon Copy Cloner with the option 'make bootable' selected.
PROBLEM: I can't boot OS X using my clone on the external drive.
I'VE TRIED:
1. holding down Command-Option-Shift-Delete while booting to bypass the internal drive. (This didn't work: I saw an os 9 icon blinking/alternating with a question mark for a while, and then the computer booted from the internal hard disk.)
2. holding down Option to select the external drive in Startup Manager. (Didn't work either: Startup Manager opened fine, but only showed my internal drive volume. I tried clicking the 'rescan' button, but it couldn't find my external drive.)
3. SELECTING THE EXTERNAL DRIVE under Startup Disk in System Preferences. Note that the external drive volume *did show up* there. So under some conditions at least, the external volume is identified as a bootable volume. (This didn't work either, though: When I shut down the computer and booted up with the external drive connected, it still booted up from the internal drive.)
POSSIBLE EXPLANATION?
My external drive is partitioned into three partitions of different formats:
1. "Mac OS X Extended (Journaled)"
2. "Mac OS X Extended (Journaled)"
3. "MS-DOS File System (FAT32)"
The bootable volume is the first partition with the os x format.
Could my problem be caused by this partitioning of my external drive?
Either way, what to do?? I hope some of you savvy people out there can help me out.
Cheers,
Philip

Hi Philip,
My problem has been fixed, & I imagine it's the same for you...:
With the excellent help from Dave Nanian at shirtpocket.com - the developer of 'SuperDuper!' (thanks Dave - you rock!), the problem (as Michael suggested) is to do with the Partition Scheme of the drive.
If your drive was like my portable LaCie Porsche drive, it was FAT32-formatted for PC out of the box. This format has an underlying MBR (master boot record) partition-scheme. When re-partitioning a drive in 'Disk Utility', the original partition-scheme sticks, so if you simply re-partition the drive to Mac OS Extended, it will still have an MBR partition scheme... which Macs cannot boot from!
For a Power PC Mac to be able to boot from an external firewire drive, the drive MUST have an APM (Apple Partition Map) Partition Scheme underlying the Mac OS Extended partitions. To do this, click on the 'Options' button in 'Disk Utility' when on the 'Partition' page before partitioning. You will see the options:
GUID Partition Table (for Intel Macs... (n.b. Power PC's cannot boot from a GPT drive))
Apple Partition Map (to create a bootable drive for a Power PC Mac)
Master Boot Record (to create a bootable PC drive)
So.... to make your external drive bootable for your Powerbook G4, choose 'Apple Partition Map' in the 'Options' page prior to partitioning.
Special note about Intel Macs: Contrary to info supplied by Apple, an Intel Mac CAN boot from an APM-partitioned drive (this is why the OSX installer can be univerally bootable!), BUT, the problem is that the OSX installer will NOT let you install OSX-intel on an APM-partitioned drive....
You can, however, clone an Intel-Mac-OSX internal drive that has a GPT partition-scheme (using CCC or SuperDuper) to an external drive with APM, & the Intel Mac will still be able to boot from that clone...
The only real use for doing this, though, is if you want a multi-partitioned backup drive with separate bootable partitions for OSX-PPC & OSX-Intel machines. (Remember that a PPC machine cannot boot from a GTP-partion-scheme drive, hence the need to use APM in this instance seeing as the Partition Scheme applies to the entire drive (it can't be different for each partition.)
Good luck - let us know how you get on!
Jason

Since 10.8 crackle / distortion on external FireWire soundcard when playing music (only when Mail is running)

Since updating to Mountain Lion I have crackles in music playback with Mail app under the following conditions:
- Mid 2009 MBPro
- external FireWire soudcard / recording device ESI Durafire is connected
- a pair of studio monitors connected to audio out on this device
- Firefox is running
- Mail app is started
- music is playing back (with iTunes or Spotify)
- navigating or clicking with mouse (or trackpad) into Mail or from Mail to another app it produces a short crackle / distortion in the music
- crazy but true: when the loudness in the song itself (not via the volume-switch) increases or decreases the crackle is getting louder or less louder, too!
- when closing Mail app, crackling is gone at once
- when stopping music, crackling is gone at once, too
- happens with no other app then Mail
Any ideas?

Welcome to Apple Communities
Open Disk Utility and repair permissions. Go to System Preferences > Users and Groups, create an user and see if it appears

Home Folder on external firewire drive

I copied my home folder to my external firewire drive and used the Advanced Settings in Accounts to redirect the Volume path to the location of my new home folder.
All worked well for about a week and then for some reason the path to the home folder was renamed and was una ble to be accessed at login. I had to reinstall SL and then redirected the Home folder path back to the external drive. All worked OK for about a day and then the same issue arose.
It looks like SL is renaming the volume from "/Volumes/WD 4TB/minimac" to "/Volumes/WD 4TB 1/minimac".
Basically it is adding a 1 after the WD 4TB
When I try to edit the path in the Advanced Options in Accounts it still is unable to find the original volume.
To date the only way I can fix it is to do a clean install of SL and redirect the home folder to the external drive.
Any suggestion to stop the volme changing name?

drive name changing usually happens when an external drive is not unmounted cleanly or if an application tries to write to that drive when it's not there. then a phantom drive is often created. in finder go to go menu->go to folder and in the resulting popup enter /Volumes
this will open /Volumes in a finder window. that folder contains mount points for all your drives. they look like aliases. there may also be a phantom drive with the name of the external which looks like a regular folder.
this phantom drive is the problem. when finder tries to mount the external and sees that there is already something by that name in /volumes it adds 1 to the name of the mount point of the external to differentiate it from the already existing item.
delete the folder for the phantom drive form /volumes and remount the external. it will mount without 1 at the end. of course this might happen again in the future and you might have to repeat the procedure. as I said, the main reason why this happens is when a drive is not unmounted properly.
Message was edited by: V.K.

Should I be able to boot from external firewire disk?

Yesterday, to prepare for upgrading to Leopard, I copied across my hard drive contents onto an external Firewire drive, by using drag & drop, folder by folder.
I was hoping that this would let me (after a reboot) select the external drive as my Startup Disk in System Prefs, or allow me to choose it if I rebooted holding down the alt key. However the external drive doesn't show up in either case.
Is there something else I need to do to allow booting via external Firewire? Is that even possible on my PB 1.5GHz (OSX 10.3.9)? Thanks.

Close, but no cigar! Copying by drag n drop misses invisible files necessary for a boot volume. The way to do this is to use one of the cloning programs like SuperDuper! or Carbon Copy Cloner to copy everything needed to make the FW drive bootable. You can even specify to NOT copy all your files if you wish.
I go to Versiontracker.com to get these programs.

Blue screen of death when La Cie external firewire drive connected

I tested a LaCie external firewire drive on my iMac and it worked fine. I packed it up well and posted it to a friend who gets the blue screen of death when the LaCie is connected to her iMac. She's not even trying to boot from it.
My iMac is 9.1 and hers is 8.1. We are both running Snow Leopard. Was there some problem once upon a time with chipsets or am I mis-remembering?
TIA

Create an ISO (Encore) or folder on your hard drive (Encore or Premiere Elements) and then use the FREE http://www.imgburn.com/index.php?act=download to write files or folders or ISO to disc for DVD or BluRay (send the author a PayPal donation if you like his program)
Imgburn will read the ACTUAL disc brand from the disc, which is not always the same as the box label (Memorex is notorious for buying "anything" and putting it inside a Memorex box)
When you write to disc with Imgburn, use the SLOWEST possible speed setting, so your burner has the best chance to create "good, well formed" laser burn holes... since no player is required to read a burned disc, having a "good" one from a high quality blank will help

Disk Utility Unable to Repair External FireWire Hard Disk

Hello all.
This is the External FireWire Hard Disk that has been giving me problems for days, it is a Backup/Clone Disk of my sis's Mac mini Core Duo, and may explain why it was so hard and took so much pain to copy some of the data out, at times it failed to mount, and I manage to rescue some data after using Disk Warrior, but Disk Warrior was also unable to replace it with a new directory.
Anyway, so I (was able to) mount the hard disk, and I was successful in erase and reformating it.
But when I (try to) repair it with Disk Utility's First Aid, this report is what I get:
(The usual 'Checking...' text lines, text in BOLD indicates RED colour text)
Checking HFS Plus volume
Checking Extents Overflow file
Checking Catalog file
Checking Catalog hierarchy
Checking volume bitmap
Volume Bit Map needs minor repair
Checking volume information
The volume Untitled could not be repaired after 3 attempts
Error: The underlying task reported failure on exit
1 HFS volume checked
1 volume could not be repaired because of an error
Repair attempted on 1 volume
1 volume could not be repaired
Then a window dropped down from the top says:
First Aid failed
Disk Utility stopped repairing "Untitled" because the following error was encountered:
The underlying task reported failure on exit
(OK Button)
I guess this hard disk is really a gone case?? I am quite OK just to replace it with a brand new one... maybe all the trouble I had in the beginning is because I may already have a faulty backup drive to begin with???
Thanks and cheers

Hi Kappy,
I knew there was something about "not mixing" PPC and Intel versions of dealing with the external drive.
The drive was originally prepared on an Intel Mac mini Core Duo. But it should also mount normally on a PPC mac as an external hard drive right?
Here's the sequence of events:
1. Tried to boot from the Back Up/Clone Drive of the Mac mini Core Duo, through my MacBook Core 2 Duo, but failed to boot up
I had to shut down the MacBook (prolonged Bluescreen)
2. When I reboot the MacBook, and tried to mount the ext drive as normal, nothing happens, I knew something was wrong
3. Able to reach the vendor, use the Mac mini again to erase and reformat the drive, then check with DU, everything is OK
Clone with SuperDuper
After that check again with DU, not everything is alright, there are errors.
4. Brought the drive home, try to mount on my iMac G5, nothing happens.
I did a check on this forum, and the reply was that I should be able to use Disk Warrior 4 (Universal) on a PPC to fix an Intel-based ext drive. I was very specific and detail in my post/question
5. So anyway, I have no other option, I ran Disk Warrior 4 from my PPC iMac G5 and scan the ext drive, trying to fix it.
It reported the drive is too damaged to be replace with a new Directory, but gave me a Preview Mode. I use this to copy some data out.
But not sure if the data is OK or not.
6. After that, I was able to mount the drive in my iMac G5, so I just use DU and erase and reformat the drive, with Zero Data
7. Ran DU again, and that's where I am now, at the very first post, getting error messages that I cannot fix the drive
Thanks and cheers

Unable to create volume - error message when exporting

Hello - relatively new Mac and iphoto user here.
I'm trying to export photos from iphoto to a 2 GB thumb drive. I keep getting the error message "unable to create volume" when I try to move anything but very small batches of photos over. What's going on? I tried to create a folder on my desktop for the photos but then when I try to move from there I get an error message telling me the photo "is in use" and can't be moved to the thumb drive.
I would move them to my external hard drive but I'm having trouble with it too. It won't even show up. When I run a disk utility on it it says it can't be verified. Sigh. So that's a whole other issue that will probably take something like Disk Warrior to clean up.
In the meantime, I'm trying to move images to the thumb drive then I'm putting the thumb drive in my other computer and moving the images from the thumb drive to it's external hard drive A long process when you can only move about 20 images at a time from iphoto.
I'm just trying to move a good bit of old photos out of iphoto on the Mace because I'm scared that the program or even my entire computer is going to crash and I'm going to have data loss.
What can I do about the "unable to create volume" message? And what's with the "file in use" error message when I try to move the images off a file folder on the desktop.
Is there a better way to move 1GB of photos all at once to the thumb drive?

Welcome to the Apple Discussions.
Seems to be two issues complicating things here:
I'm trying to export photos from iphoto to a 2 GB thumb drive. I keep getting the error message "unable to create volume" when I try to move anything but very small batches of photos over.
What format is that wee drive? Mostly there are FAT16 or FAT 32 and there is a limit to the number of objects they can have on the root of the drive. The workaround is to export to a Folder on the desktop and copy that over.
Which brings us to:
I tried to create a folder on my desktop for the photos but then when I try to move from there I get an error message telling me the photo "is in use" and can't be moved to the thumb drive.
You will sometimes get this message when you try to export two files +with the same name+ to a Folder. As you know your camera is well capable of producing many files called something like DSC_1234.jpeg. In iPhoto these will be in separate folders, so no problem. However, when you go to export them to the Folder on the desktop if iPhoto continues the export one will overwrite the error.
Solution: Give the Pics a title (Photos -> Batch Change) and a sequential number. Then when you export, in the export dialogue you have the option to use the Title as filename.
Regards
TD

Cannot Boot from OSX on external firewire drive

I recently bought a seagate hardrive and installed it in an external firewire casing. I partitioned it into two partitions, and installed osx 10.4.10 on one of the partitions, the same as is running on my Ti Book.
I tried selecting the os on the firewire drive as the startup disk, but when i restart, after the grey screen i get the flashing question mark icon, until the mac recognises only the default osx on the internal drive and boots with that instead.
That not working, i created a clone of my startup disk using DejaVu in my system preferences and saved it on the other, empty partition on the external drive and tried booting from that.
On restarting, i get the grey screen once again as the backlight fires up, and nothing more. the screen remains grey without any further ado until i hold the power button and force it to turn off. then as i start it up again, up comes the flashing question mark icon followed by a boot from the internal drive.
Any Solutions on this?
Many Thanks, Neptune.

Hi Dale,
Whoops- everythings not as smooth as i thought it was!
since i restored my internal drive, a lot of things have been really messed up, starting with, for example, iTunes reverting to version 4 instead of 7. that wasnt a problem, i still had the 7 installer, and soon had my whole music library back again. but the computer appears to have a problem with the handling of graphics. the finder wont create previews of even simple jpeg images, nor will it for video. quicktime wont open any video file, i get some random error message which i cant remember stating it could not open the file. and if i view my finder window in grid icon view, the usual blue mac os desktop image that i keep as a background in the finder window isnt there, instead its pitch black. same goes for the slideshow feature in the application graphic converter, i can start a slideshow and it will scroll through the images, but every image will instead be completely black. there are no scroll bars in itunes. i can scroll down randomly by clicking where the scroll bar should be, but there is nothing visual there at all, no scroll bar, no arrows. when i connect my ipod, the main ipod window of itunes wont display any graphics either, be it the picture of the ipod or the capacity bar indicating usage of the drive for music, videos, data, etc. instead, fine print says something similar to 'cannot display image, quicktime and lzw tiff decompression plugin (?) required' I cant remember word for word what it says, dont quote me on that.
the computer also came to a dead freeze twice in ten minutes, i had to hold the power button down to get it to shut off.
im sure there are other issues too which i havent yet noticed, but even these, i havent the faintest clue what could be causing them!
do you?

Booting my imac from an external firewire drive suddenly stopped working. Disk still mounts but it will not boot the machine!

I took my MacBook Pro in for repairs and erased the drive for safety AFTER having copied the entire contents to an external firewire 800 drive using SuperDuper!
The copy process made the disk bootable and I was able to boot up my iMac and run it just as if I were working on my MacBook Pro. After a couple of times working this way, the iMac stopped booting from my drive.
The drive shows up when starting up by pressing the option key but then, after a long time, the iMac shows a circle/slash symbol as if it can't find the system files.
If I restart without pressing the option key, the disk mounts on the desktop and I can use it as an external drive just fine! I tried selecting it in System Preferences as the startup disk, but the same thing happens, blank grey screen with the circle/slash.
Since this happened with a Seagat drive - a brand that has failed me in the past many times - I thought it was a disk problem. I had backed up my MacBook pro contents to another Toshiba drive, and booted from there perfectly well for a couple of times...
Until the same thing happened! Thank God I didn't trash the Seagate although it makes very faint clicking noises that will keep me far away from using it again anyway... but that's another story!
iMac runs 10.5.8, the boot disk (and my MacBook) runs on 10.6.8 if that makes any difference... And now I'm scared that when I copy back to my MacBook Pro it might not boot up at all!!!
What gives???
- MerlinCreative

You need to reinstall Snow Leopard onto the external drive:
Reinstall OS X without erasing the drive
Do the following:
1. Repair the Hard Drive and Permissions
Boot from your Snow Leopard Installer disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities menu. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the installer.
If DU reports errors it cannot fix, then you will need Disk Warrior and/or Tech Tool Pro to repair the drive. If you don't have either of them or if neither of them can fix the drive, then you will need to reformat the drive and reinstall OS X.
2. Reinstall Snow Leopard
If the drive is OK then quit DU and return to the installer. Proceed with reinstalling OS X. Note that the Snow Leopard installer will not erase your drive or disturb your files. After installing a fresh copy of OS X the installer will move your Home folder, third-party applications, support items, and network preferences into the newly installed system.
Download and install the Combo Updater for the version you prefer from support.apple.com/downloads/.

Creating Volume on External Firewire HD

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