Avoid Windows Dynamic Disks

Microsoft's implementation of software RAID leaves much to be desired, but the very worst is this odd thing known as "Dynamic Disks". Getting right to the point - if you use dynamic disks sooner or later you will be faced with this:

And then you will learn that the dynamic disk is a liability, not a help.

The above screen shot was taken for a disk on a server that had no hardware problems. The hard drive was less than a month old; it tested clean on a deep surface analysis using SpinRite 6. The memory tested clean using memtest86. A fresh load of Windows XP on that same system functioned flawlessly. In fact the system was running for some days and the above problem only showed itself when an attempt was made to reboot. The result? Massive. File. Loss. Thousands, in fact, and a long weekend spent on data recovery and restoration.

But of course, anything can and will fail. That's not the point. The problem begins in that the majority of file management, partitioning, disk copying, and data recovery tools don't work very well when used on dynamic disks.

As an example, my favorite way to clone a hard drive is to connect both the old and new hard drives to a Linux box and type:

        dd bs=8k if=/dev/hda of=/dev/hdc

This works every time. Or so I thought until I tried it on that "unreadable" dynamic disk. The resulting disk shows up as "foreign". I've not bothered to research what "foreign" means but evidently it's a synonym for "useless".

I'm no stranger to data recovery but even after I acquired some tools that could cope with the dynamic disk the results were still far from satisfactory.

And all this on a disk that was perfectly serviceable.

In summary:

• Dynamic disks are fragile.
• Dynamic disks tend to mask problems that could otherwise be found and fixed early.
• Basic partitions can rightly be considered an open standard (widely used, well understood, transparent, robust).
• Dynamic disks should be viewed (with suspicion) as proprietary and closed.
• Most disk and partitioning tools don't work (or don't work well) when used with dynamic disks.

What's the alternative?

Dynamic disks were created as a foundation of software RAID on Microsoft's "Professional" and "Server" products. So too many systems are using them for that reason. But they're not at all necessary as hardware-level RAID that is inexpensive, full featured and very reliable is readily available. (I've had good results with controllers from 3ware and Adaptec as well as motherboard chipset RAID from Intel. There are others also.)

Note that the above recommendation to use hardware RAID does not apply to Linux. Software RAID on Linux has been well proven and is open and well understood. And it works within the confines of normal hard drive partitions. Hardware RAID also works well with Linux - proving, once again, that open source software provides more and better choices.

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