Q

How to prevent drive corruption in the event of power failure

In this Ask the Expert Q&A, learn how a PDA device stores data and programs. Also learn how Compact Flash cards and hard drives differ and what some are doing to prevent drive corruption in the event of power failure.

If I install an OS on a Flash card, will it help me avoid file system corruption due to frequent power failure?
I am afraid the answer is no. Don't assume that because your PDA doesn't have a hard drive, can be turned on and off without shutting down, and always restarts correctly, that you can replicate this by installing your OS onto a Flash card. A PDA stores its OS and basic programs in a read-only memory (ROM) chip. This ROM chip remains unharmed even if the machine shuts down unexpectedly. Any data and programs that get added later are stored in the device's random-access memory (RAM). This is only available when the device is turned on. Data can be stored in a PDA's RAM because it continues to draw a small amount of power from the batteries even when the device is turned off. Some newer PDAs use flash memory instead of RAM. Flash memory is non-volatile. This means it preserves the data and applications it stores even when the battery power is depleted.

You could install your OS on a Compact Flash (CF) card, which has certain advantages over a hard drive. CF cards

are faster, use less power, produce less heat and have no moving parts because they are solid-state devices. They also have a wider operating temperature range than disk drives, which can fail from vibration, heat, cold or shock. They are also more tolerant of power failures during write cycles than a standard hard drive. However, a power failure during write operations can corrupt a boot sector or File Allocation Tables used in the FAT file system.

It's important to note that CF cards only support a limited number of writes and over time it will fail. This limits your ability to use it like a regular hard disk with an operating system installed on it. For example, if you located the Windows swap file on it or enabled logging for all events, you would eventually wear out the card. There is a version of Windows XP called XPe (embedded), which enables you to reduce the number of writes XP makes to the card. You can download XPe SP2 from http://msdn.microsoft.com/embedded/windowsxpembedded/default.aspx.

You may be interested in SiliconSystems' PowerArmor technology (www.semiconductorstore.com/Pages/Products/SiliconSystems.htm) used in its solid-state storage products to eliminate drive corruption in the event of a less than graceful power-down, though they are aimed at the high system end of the communications, military, and medical markets.


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  • This was first published in September 2005

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