Raid Volume Rebuild

How To: Steps to take on a failed RAID-1 array, where one drive appears to have failed. This article assumes you have previously installed an Intel Desktop mirrored RAID array with two disks.

Related Article: Desktop RAID-1 Mirrors - Installation

Note: Many searches arriving at this article are asking this question: "Can you reboot a workstation while the RAID is rebuilding?" The short answer is yes, but the RAID rebuild will start over and the drives are at risk. It is best to leave the computer on. See below for other details.

The other question: "Can I use the computer while the RAID is rebuilding?" Yes, with no restrictions.


When a Desktop's mirrored Raid reports a "degraded" or more commonly a "failed" drive, it sounds like a horrible calamity, when in fact, it is probably a minor event -- but it may still require your attention. In a RAID, the computer has 2 "mirrored" hard drives, where one drive is copy of the other. If either fails, the other will continue operating as-if nothing was wrong. When a RAID fails, one of the drives is out-of-sync, or more rarely, failed.

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When a RAID fails, it is seldom a physical failure

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Reasons:

Usually an array goes south when there has been a power failure or the operating system has crashed (hence why I had to write this article). Opponents of RAID would say, "see, this is why you shouldn't bother with RAID; half the time it is the problem." I counter by saying with only one disk, the odds of corrupting it are much higher and rebuilding the RAID is easy. When the computer goes down hard, logical damage to the disk is likely.

But almost always there is no physical damage -- usually one of the drives just became "out-of-sync" with the other.

Symptoms:

The Windows System tray shows a failed Raid, with one of several possible messages. For example, an Intel RAID controller, commonly found on almost all desktop computers from the past several years, shows a two-disk drive icon (the mirror), where one is red.

This illustration shows a failed array that is in the process of rebuilding

• If it shows "Degraded," it is in the process of rebuilding and there is nothing you need to do but wait. I would leave the computer running while it rebuilds. You can still work, open files and surf the net while this is happening.
  
• A "Failed" drive requires action on your part; follow the steps outlined in this article.

Steps:

1. In the System Tray (you may need to show hidden icons); choose the RAID icon.

If you do not have this icon, look in the Start Menu "Intel Matrix Storage Manager" or "Intel Rapid Storage Manager." You can confirm the program is installed by looking in the Control Panel's 'Programs and Features' Add-Remove. (Since this article was written, this utility was renamed from "Intel Matrix Storage" to "Intel Rapid Storage Technology; see download link at the end of this article)

2. "Mark the failed drive": Once the panel opens, tunnel down the tree, locating the failed drive.

"Other-mouse-click" and choose "Mark as Normal".

This should start the rebuild. The System Tray icon will show "A RAID volume is being rebuilt. Data redundancy is being restored."

Click the image for a larger view; click right-x to return

3. Watch the progress by opening the Volumes folder (illustration above, locating the Yellow icon). Other-mouse-click and choose "Show Rebuild Progress".

The indicated time is a reasonable estimate and a 1Terabyte drive can take about 1.5hrs to rebuild.


While Rebuilding - Rebooting, etc.:

While the RAID is rebuilding, you can still use the computer as you would normally, but it is best (but not required) that you leave the machine powered on until the rebuild completes. During this time, the computer may behave a little slower and there will be much disk activity.

If you shut-down the computer, the rebuild starts over on the next reboot. If you do power-down the computer, the remaining drive, however unlikely, is at risk for a failure. If power-problems have caused the RAID to fail, be careful about stopping the RAID rebuild prematurely.

Also, if the computer goes to sleep, the rebuild is also suspended. Consider disabling the Screen-savers during the rebuild.


Performance Improvement: Hard Disk Cache

If the RAID is rebuilding too slowly (more than 4 hours), check the local Hard Disk Cache setting.

• From the Storage Management Console, open the Volumes folder.
  
• Other-mouse-click "SysRaid" and choose "Enable Volume Write-Back Cache". This change can be made on the fly.
  
• Alternately, this same setting can be found in Control Panel, Disk Drives, locate the hard disk "SysRaid", select Properties, "[x] Enable Write Caching on the Device."

This setting changed my Rebuild from 4 hours to 1.5 hours. This same setting has other benefits and all disk-IO activity will be faster.

Really Long Rebuild Times:

Before looking at these steps, be sure to see the section directly above.
Some readers have reported 80+ hours on a 1Terabyte rebuild. I am waiting on their reply to see if the cache-setting (above) helped the problem and your help in this is welcome.

I would wonder if the machine were infected with Viruses. Consider disconnecting the network cable, then disable the virus scanner and try the rebuild again. If this does not improve the rebuild times, leave the RAID broken while you do a more thorough test for viruses. Consider this Keyliner virus article: Removing Win-Viruses.


More Serious RAID Failures:

Sometimes, rarely, after a particularly brutal power failure, the motherboard may not be able to detect the "failed" drive. In the Matrix-software, you may not see the failed drive.

Try these steps:

a. Power off the computer and disconnect the failed drive. (Use the utility to see the drive's serial-number).

b. Boot the computer, then shut down normally.

c. Re-connect the failed drive and attempt the rebuild again.

(Note: This power-off/disconnect solution has not helped those with 80+ hour rebuilds.)


Re-Occurring Problems:

If the RAID array fails frequently, there could be several causes. Consider the following, where the most common are listed first:

• Bad power; intermittent power; low-voltage power; get a UPS.
• A weak PC powersupply (replace/uprgrade to a larger supply)
• Failing circuitry on the main motherboard (especially if you have been having power problems)
• An actual drive failure

If the drive has physically failed (note: I have not seen a real failed drive in many years; it seems much rarer than it was in the mid to late 90's), you must replace it with a similar drive with the same capacity (or larger).

The replacement drive does not have to be the same brand and model (although that is my preference, when possible).

RAID is not a Cure-all

Remember, a RAID does not protect you from having to do backups. It will not protect your data if a virus strikes, the computer is stolen, or the house burns down. Here is where an off-site backup is nice to have.

Consider the RAID as insurance against a drive failure (which is admittedly rare). More likely, it is insurance against a corrupted disk due to power-failures and other hard crashes. As I had discovered this week, a power failure caused one drive to depart while the second survived. The RAID saw the problem and still allowed the computer to boot.

This was the behavior I wanted to see during this type of event. I will never know if a single drive would have survived the outage, but I do know all was safe. I simply re-built the RAID and was back to normal a few hours later with nothing more than a few mouse clicks.


Related articles:
Desktop RAID-1 Mirrors - Installation
Acronis vs Ghost
Maxtor External USB

Links:
Intel Download Page (Choose your operating system and computer for best results)

As of 2010.08:
Intel Download: Rapid Storage Technology (SATA ver 9.6.0.1014 2010.03.23 formerly called Intel Storage Manager. Choose the 'AllOS' version, at the bottom)