Greetings fellow Linux aficionados.

My Situation:
I want to use an external hard drive as a storage medium for backups for four different operating systems: Windows 7, Windows XP, Fedora Core, and CentOS 5.6. These OS's reside on two separate boxes, one of which is a multiple-boot box. It would be really nice if I could use the same physical device for all of my OS's. My heart leans toward a large capacity drive like a 2TB device. A pre-made solution like a Western Digital MyBook or Fantom Drive would seem preferrable, but a custom-built device is not out of the question.

My first consideration is to use a 2TB WD MyBook or similar and reformat it with a filesystem that both Windows and Linux could use without conflicts. But it appears that Windows 7 may be a "problem child" and not be compatible with the other OS's.

My alternative consideration is to format the device with two partitions and format one with NTFS and the other with Ext3. This is where I get a bit confused. I have, in the past, reformatted USB drives with another filesystem without issues. But I never tried to repartition a USB drive. I don't know how Windows nor Linux will react to mounting a multi-partitioned USB drive. Then there is some confusion on my part about the eccentric nature of high-capacity drives. Among the 2TB drives, there are mentions of "advanced formatting" and "alignment programs for XP" that make me reluctant to use anything bigger than 1TB.

Then my consideration of last-resort is to use an external docking station and multiple 1TB drives, but this is the most expensive approach of all.

My Question:
Has anyone managed to successfully put multiple partitions on a USB external hard drive and have it behave in both Windows and Linux?

Pointers and/or suggestions are most welcome.
Thank you for your time and attention to my query.

Hi there,

that's not what I would prefer - I'd rather have separate physical media. But that is -to some degree- a matter of personal preference.

What do you mean, "custom-built"? Are you regarding a combination of an off-the-shelf HDD and a generic USB enclosure "custom-built"? I don't.
But nonetheless, that's not relevant for your question.

That depends. It depends on your choice of file systems. All the OS's you mentioned can deal with FAT32, which is simple and robust. So that would be a good choice if it weren't for a little stipulation: FAT32 doesn't support files >4GB. If you have files that large (or cannot completely rule out that you may have), FAT32 is not an option for you.
Second, all these systems should be able to deal with NTFS, though there may be some issues here and there with the Linux OS's. After all, NTFS is still closed-source, and all work that the Linux programmers could do so far is based on reverse engineering, guesswork and testing.
Finally, there is Ext2IFS for Windows - that's a file system driver that makes Ext2/Ext3 file systems accessible from Windows. I've used it with XP for some time and that worked fine; I'm not sure, however, if it is compatible with Seven.

That's absolutely no problem. Both Windows *and* Linux will do nicely with USB storage units that have multiple partitions. Windows will assign a drive letter to only the partitions with a file system it recognizes, but that's not a problem; Linux will probably recognize all partitions, so you can mount them as separate file systems (if your distro doesn't auto-mount them to /media/volume-id anyway).

Never heard of those issues, but a good friend of mine is using 2GB external drives with XP and Seven, and he never mentioned that there was a problem about that.

It definitely is. If you go that far, it may be cheaper to "reanimate" an old PC and set it up as a file server with multiple HDDs.

AFAIK that's no problem at all. YMMV.

[X] Doc CPU

Thanks, Doc, for the response.

In regards to the choice of filesystems:
FAT32 is not an option. Files sizes could easily bust the 4GB limit, especially with disk image files.

NTFS for XP and Linux works well, but Win7, I suspect, may use features not covered by the current NTFS-3G driver. When it comes to Linux compatibilty with anything Microsoft, I don't trust Microsoft to "play nice". Linux is a competitor.

Ext2IFS works well, but Win7 does not want to install it because of a missing digital signature. Win7 can be forced to install it, but I prefer not to do that right now. The Ext2IFS's author is aware of this issue and claims that a fix is "coming soon".


In regards to multi-partitioned mounting:
Good! I can probably put that concern to bed.


In regards to the high-capacity drive issues:
All of this eccentric stuff about high-capacity drives, I got from digesting hard drive specs, especially Samsung drives. Most manufacturers claim to use all sorts of advanced magic tricks to squeeze the last byte out of existing technology. It may not be anything except tech-talk to impress the potential buyer, but if not, can it be an issue with partitioning and/or formatting? My knowledge of modern hardware is limited, but growing.


In regards to reanimating an old pc:
Considering that a good docking station with USB2 and eSATA interfaces costs about $30-35, I doubt a retrofit of my old Dell box with SATA would be cost-effective.

Hi there again,

yea, I see. That's why I mentioned this limit. I encountered it a few times dealing with MPEG2 video files, but disk images are another issue.

Wait a moment! Maybe you didn't get the idea down to the detail.
Yes, it's true that Seven's NTFS driver is more advanced than that of XP, and has some extra functions and features (though they claim to use the same NTFS spec Version 3.1). But you don't have to use those features, do you? ;-)
Acutally, I'm using an older 250GB HDD that I formatted to NTFS under Windows 2000, and I can use it without trouble with Win 2000, Win XP, Win 7, Ubuntu 9.04 and Ubuntu 10.10. Probably with any other distro using NTFS-3G.

I GUESS: When a partition is NTFS-formatted under Windows, it gets tagged with the Windows version. If you access it with a later version, it will refrain from using its own more advanced features. But again, that's just a guess of mine based on the experience that there's really perfect backwards compatibility.

Wanna give it a try? Maybe with Seven installed in a VM? Maybe I'll do that some time, and I expect Ext2IFS to work fine. But then again, I'm not keen on touching that piece of crap (Win7) unless really necessary, and not without protective gloves ...

When I read your mention of these issues, I tried to think of technical limits that might apply. But at that capacity region, there's none that I know of (which doesn't mean anything). The highest limit I know is that some old mainboards (BIOSes, actually) have trouble with drives >128GB (and I mean drives, not partitions).
That very same limit also applied to some old OS's, the latest of which was Windows 98 (98SE overcame the 128GB limit).

AFAIS no. The interaction between OS (or BIOS during the first boot phase) is a matter of requesting sectors to be read or written, and the sectors are referred to by their number. Since the sector size is usually 512 byte, a 1TB drive has about 2^31 sectors, a 2TB drive has 2^32 (roughly). According to SATA and the latest ATA spec, the sector number is exchanged as a 48bit quantity, so we're far from that limit.
However, it's possible that there is an implementation specific limit with some controllers, especially the cheap USB/SATA bridges. I admit that 2^31 or 2^32 rings a bell. Possibly some embedded-system programmers didn't care to *use* more than 32bit ...
But that would be a limit of the controller hardware, not the OS's used to access the drive.

Oh, depends on whether the old machine is still working or not. My motto is: If a piece of hardware is still intact and just resting in a quiet corner, why not put it to use again? Of course, spending $100 or more to get an old system up and running would be nonsense. But if it's just a matter of a few hours' work, why not? From a business point of view, that's foolish, too, but in the home and hobby field ...
By the way, I've never seen a USB enclosure that hosts more than one drive at the price you mention. Here in Germany, they would usually start at far beyond 50 Euros - at a very rough guess, that's about $70 and up. The single-drive enclosures typically start at about 20 Euros (~ $30).

[X] Doc CPU

Thanks again, Doc, for the reply.

I think I allowed myself to become entangled in a lot of hard drive specification details that confused me. After much consideration, I understand that external and internal HDDs are pretty much functionaly equivalent. And drive capacity doesn't matter either except when you break the 2.2TB limit and you must use the GUID Partition Table stuff. So I now know what I will do from the hardware perspective.

However, I am still researching what I will do with drive partitions and the filesystems that will reside on them. I will do some experimentation with NTFS-3G and Ext2IFS as you suggest.

This will be my last post to this thread unless I find something worthy of an update.

how about considering exFAT? its the next version of fat32 without the 4gb limitation.

win7 = already supported
xp = must be sp3 and there is a small 300kb downloadable patch that will allow it to access exFAT.
fedora = a patch is available depending on your version
centos = a patch is available depending on your version


For your needs; I'd recommend a NAS so that:
1. you don't have to unplug and replug the usb external hd between the machines.
2. you can access the data via a web browser and/or access it via a shared folder and/or mount it to look like a local partition.
3. always on; ease of use. you don't have to be physically there to move data around the 4 machines; since all can access it all the time.

Hi there,

I've heard of exFAT, but nothing yet that I could get a grip on. As it appears to me, it's still highly experimental. I wouldn't like to use it on a disk or with a machine that I need for my everyday work. Maybe on a computer set aside for testing.

That's pretty close to what I had in mind when I suggested to put an old machine to a new purpose.
My solution, however, is a low-energy PC based on an Intel Atom CPU that needs only about 20W. It has an internal 160GB SATAN drive, an external 1TB USB drive, runs on Gentoo and offers a samba file server, Apache and mySQL, a local mail server, and a lot more services. Plus, I temporarily connect and mount either of two more 1TB drives via USB for backup purposes and store them in a different place otherwise.

I wouldn't call that a typical setup, however. ;-)

[X] Doc CPU