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Use Bad Block Frequency to Determine a RAID 5 Stale Drive

We have been discussing the love affair I have with stale drives in a RAID five array and how best to determine if in fact one exists. I explained how the NTFS file system data is normally laid out and the fact that the old and new data, as well as how long the drive may have been in the array play a significant role in finding the correct stale drive.

The next step in our “Search for the Stale Drive” is to use the RAID Diagnostic Toolkit to scan all of the drives. From the menu bar “Configuration” option select “Populate Stream List”. This function will scan the current system you are working on for all hard drives including ones tied to a USB device. These devices will be listed in the “Stream List”. If you are working from images then from the same “Configuration” option on the menu bar select “Add File To Stream List”. A standard Microsoft Windows file selection dialog box will appear. You may then use that to add your images to the “Stream List”.

Once all of the streams have been placed in the “Stream List” list box, double click on each one that is part of your RAID 5 array. As you double click each stream object, it will be placed into the “RAID Configuration” list box. Please be sure to place the streams in order in the “RAID Configuration” list box as it will help in determining which drive is stale.

I can offer this clue: in a stacked set of drives that have been residing in a cage several things happen. The outside drives remain the coolest for two reasons: first, they have unrestricted air flow across at least one side of the drive, and secondly dust has a more difficult time collecting and obstructing air flow. This fact alone is one of the main reasons why the interior drives seem to fail before the outside drives do as the inside drives have restricted air flow.

Another thing that happens is the interior drives have heat coming not only generated by them, but they have heat from the drives that are next to them. This can exacerbate an already poor air flow problem and cause an early fault for the hardware.

As a brief aside, the reason why heat is bad for a hard drive is multifold but there are two main points: first, each hard drive has a motor and that motor has some type of lubricant. If in fact the drive gets hot the lubricant can lose its viscosity and the spindle can begin to slow and cause a head crash. Secondly, heat will swell components of a hard drive, in this particular case I am referring to the platters.

Next time I will discuss how platter swelling can cause a head crash, and what to look for once the parity scan is executed.

Until next time…

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