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Can I combine two hard disk drives into a single logical drive?


Hi, I have a Dell Optiplex GX620 running WinXP 32-bit OS. I have 3.3GHz of Processor and 3GB of RAM. And a 75GB HDD. Question: I am wondering if I add a second hard disk to my computer to have more space, is there a way to have my computer read both drives as one large drive? Example: My original hard disk is 75GB, if I add a 500GB hard disk drive, can I make it where my computer has one C: drive that is the size of both hard disk drives combined?

In this excerpt from Answercast #23, I look at the problems associated with merging two drives into one. There are some better options.

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Two into one

The short answer is yes. It’s been a long time since I’ve done it, for reasons which I’ll explain in a moment.

Basically, I believe, in Disk Manager. You can select both drives and then manipulate them somehow. At least, that’s how it used to be.

Double your risk of failure

I’m going to strongly advise against doing that.

The reason is very, very simple. When you have two drives making this one logical C drive, if either of those drives fail, then your entire C drive has failed. In other words, you have doubled your risk of failure and it’s something that I strongly suggest that you not do.

If either of those drives has a problem (has a bad sector, decides to fail, whatnot), then you might think that you could replace just that drive. But,  effectively what you’ve set up is a very weak form of RAID… and you can’t.

When you end replacing that drive, you end up having to reinitialize the entire volume that you’ve created out of both drives. So, it’s not something that I recommend at all. In fact, I strongly recommend you not do this.

Two drives are better than one

There are two alternatives:

1) Live with the two drives, just live with them.

Put your operating system and so forth on C. Let that be 75 GB and then manipulate your programs so that you’re dealing with data on D which is 500 GB. That is the traditional solution. It is the supported solution; it’s the approach that most people end up taking to this kind of a problem.

The other approach… and this one I’m also a little bit reluctant to suggest, but I’ll throw it out there, not because it’s a bad solution but because my experience has found it to be slightly less than stable.

2) Go ahead and create your C and your D drives as separate drives. Then setup what’s called a mount point.

The command I’m going to point you at is a command in Windows (at least in Windows 7… I think it’s there in Windows XP as well) called: “Mountvol.” It may go by a different name in XP; potentially, plain old “Mount.”

What Mountvol allows you to do is to mount another drive into what appears to be a folder of your first drive.

For example, you could create a folder on your C drive called “D.” If you change the directory into that folder, you find the contents of the D hard drive. In other words, you would see all of the D drive as if it were a sub-folder on your C drive. The syntax for the utility is not trivial. It requires or depends on the volumes being formatted with NTFS; that is the only available format that supports having these kind of mount points involved.

My concern is that, in the past, when I tried to use it, it seemed that mount points disappeared without warning. I never could come up with a rhyme nor reason to it. And as result, I basically modified what I was doing so that I no longer relied on mounted volumes.

It is one of the approaches to getting around the 26-drive limit that’s in Windows. You can mount volumes that don’t have drive letters. Then you have a volume that contains lots and lots of different disk drives that do not suck up additional drive letters.

Like I said, it’s not necessarily simple, but if you are bent on going down this direction, I believe it is a much more appropriate direction to head than trying to take the two drives and make them appear as a single C

Do this

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5 comments on “Can I combine two hard disk drives into a single logical drive?”

  1. Unless there is some reason not to, you should consider cloning the 75GB drive to the 500GB drive. The 500GB drive would become the single large drive you seem to be looking for. The 75GB could be removed and discarded or placed in an external case to use as additional external storage.

  2. Why not simply do a disk copy from the old drive to the new larger drive, and then expand the partition to the new larger size? The old drive may serve several uses after that. It can be reformatted and used to store your data or music files. It can be used as a backup disk drive, etc. The age of the old drive might not lend itself to reliability, so adding the new drive as drive D: may not be the safest path to follow.

  3. Leo is right. It is not worth making such an elaborate arrangement (spanned, dynamic drives) to conserve a 75GB drive. Get a big HDD, image the 75GB C partition and restore it to the big drive. Then you can use the 75GB drive for whatever purpose – internally or externally.

  4. I agree that there usually isn’t any reason you can’t just use the two drives separately. However, if you really want to, there is a much easier way to create a mount point than the command-line utility. Just open ‘diskmgmt.msc’, right-click the partition on the drive, and choose “Change Drive Letter and Paths…”. From there, you can add a mount point very easily.

  5. Most of the hard disk drives I’ve purchased in recent years (Seagate, Maxtor, etc) came with software to install them that allowed an “upgrade” function. It would essentially bit-copy all of your information from your old (small) drive to your new (big) drive, then tell you when to swap them. Once the new drive is functioning successfully as C: drive for a few days, I update the backup then erased the original drive and reused the space for storage. Naturally, you should make a good backup of the original drive before starting this or ANY other upgrade scheme. And when you’re doing the backup, be sure to take the extra time to have your backup program verify the backup.


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