Thanks for your good introduction to this essential topic, Glenn. I avoid USB-only drives for myself and my tutorial clients for this and another reason: FireWire is much faster. The popular MyBook drives are the worst offenders on both counts, from my experience. It is so easy and affordable to purchase and use combo FW800/400/USB drives, there is no reason for intelligent Macintoshers to do otherwise. Macsales.com, WiebeTech.com, Verbatim.com, G-Technology.com, and other companies have fine products that I use daily. Keep this conversation going. USB-only drives are bad choices. [Nemo / MyMac.com Reviews Editor]
Isn't it going to be hard to find a firewire port soon. I thought apple was getting away from them and moving to only USB.
There's no announced plan. Some new models removed FireWire; some continued to have them.
And to expand on what Glenn said, the MacBook model that removed FireWire was discontinued and replaced with a MacBook Pro that got FireWire back. So that's a good sign for the continued survival of FireWire.
And, just in case it wasn't understood, the remaining MacBook also has a FireWire 400 port. In fact, every model except the MacBook Air has either a FW400 or FW800 port.
I had a similar issue with a friend's usb hard drive on her Leopard machine. It would not reformat as one partition. I divided it into two partitions and they formatted perfectly.
I too was able to reinitialize a pc drive as mac by partitioning it. I bought a Cavalry drive (admittedly, it is slow). I tried different strategies for two weeks to no avail. Then I discovered a technical bulletin on the manufacturers website "Repartitioning and reformatting from FAT32 to Mac OS X Extended" . The method is simple and works
I got the same "Can't allocate memory" statement. It was just as useful to me as to you. I did change the jumpers on the drive from cable select to Master and then all went well. Of course, you have to take things apart and put back together, but it worked. I then backed up the drive with no problem.
Got the suggestion from a neighbor guru type. Don't know why worked, but did.
I had a similar problem with a G-Drive Q. Switching to USB resolved the issue but the FireWire never worked. What is odd is that I have another G-Drive Q with the exact same specs that works fine on FireWire.
I have an external enclosure with 4 PATA drives in it. In 10.5 I was only able to mount these drives via the FW400 port, and even then sometimes they would not mount if I had my iSight plugged in at boot. After installing 10.6 I was able to mount the drives via FW800 and there's no conflict with the iSight.
I ran into a similar problem with an external Iomega 2.5" drive w/USB & FW400. It works fine on my MacBook Pro w/USB, but only works with FW400 on my 15-in aluminum G4 PowerBook. I attributed this to a hardware issue since the drive is powered by the port (although it has a jack for an optional power supply). Testing with an external power supply might determine if it's a hardware problem (i.e., if it starts working over USB with the PowerBook).
The problem is that most USB drives come formatted for Windows (Master Boot Record).
In Disk Utility instead of trying to Erase, select Partition, then change the Volume Scheme to 1 Partition, in Options select GUID Partition Table, now click Apply to format the disk for Mac.
That only works in some cases. This wasn't one of them. The drive was already formatted for Mac, and I tried for both the Apple and GUID partition tables.
The posts on other forums indicate that changing partition types sometimes helps, sometimes doesn't. Since booting into Tiger always helps, it's clearly a Leopard bug carried through in a different way into Snow Leopard.
It's important to look at lots of situations before making a blanket recommendation. Hence this article.
A family member bought a really cheap USB-only 500GB external hard drive upon which my wife tried to copy 35GB of photos. We needed to reformat the drive before we could copy the files. However, it showed up as "Read Only", and we couldn't erase it in Disk Utility.
By accident I ejected the drive by clicking on the eject icon in the Finder sidebar. The drive disappeared in the Finder, and the icon disappeared from the desktop.
However, Disk Utility still showed the drive as connected, and it was now able to erase and reformat the drive. We were then able to copy the data onto it. The new format was FAT-32, but I don't think that matters.
Maybe this workaround will work for you.
I find that my portable external drives don't always mount when (I think) they should. In the case of USB drives this may be due to insufficient power on the USB bus, particularly with laptop computers. For this reason I always keep an appropriate power adaptor handy for the drives - using external power usually does the trick. Sometimes a computer restart is required as well. I haven't erased any of these drives recently so I couldn't say if the power issue applies as well in this case. But it's worth considering when you're running through alternatives.
My experience is that I've solve this problem by Using Partition in Disk Utility I would have also picked the Guid Partition Map
I have found that using Partition works as well. Recently with a stubborn drive, I create a single partition set to "free space" first. When that was done, I repeated the single partition process using Mac OS Extended (Journaled) with GUID Option set. Drive is working well now. Copied over 20 GB of files as a test.
Ran into this problem today.
Bought a USB2 Seagate 1TB drive formatted for Windows NT - it showed up on the desktop fine (MacBook Pro/Leopard). So I decided to use Disk Utility to change the formatting to MAC OS extended journalled and it immediately wigged out and the drive would no longer mount. Disk Warrior could do nothing.
I decided to use my recent purchase of iPartition and it had no problemreformatting the drive and changing the partition map to Apple.
So it seems to me that, (here at least), Leopard is fine with USB drives - perhaps it is a problem specific to Disk Utility?
I have an old Formac drive with an FW400 interface where I was getting the POSIX error with Snow Leopard. After reading through the earlier comments I tried 'erasing' it on my wife's old laptop running Tiger. Worked perfectly - now mounts on SL without demur. It's only a workaround though, so I hope someone will come up with a proper Snow Leopard solution soon.
I just ran across this error. One option I found that worked for me was using the 'pdisk' command in the terminal. The steps are as follows:
1. Open Terminal
2. Type "diskutil list", that will show you the attached drives. Find the offending drive (mine was /dev/disk2)
3. Then type "pdisk /dev/disk2". Replacing whatever you got in step 2 for "/dev/disk2"
4. Then type "i", and take the default options.
5. Type "w" to write the partition map
6. Type "p" to see the partitions, one should be very large, and labled Apple_free. Mine was #2
7. Type "c" to create a partition. For first block, type 2p (or whatever number you got from step 6). For length, type the number listed under length in step 6, then type a name (If you want to make multiple partitions, enter a smaller number for the length and then repeat this step for each partition, using 3p, 4p, etc as your start)
8. Type "w" to write it, then type "q"
9. You'll get an error, but then you should be able to use Disk Util to fix it.
I had a similar problem - I couldn't persuade my disk to reformat using either firewire or USB, or using any of the other suggestions above.
I rebooted, and then managed to reformat first time - in my case, firewire, 2 partitions (1 FAT) with MBR partition table.