Deciding how to manage data loss on your RAID array

Mar 8, 2010 Chris Gurley

RAID data Recovery - Wikimedia

Should hardware failures on more than one drive occur simultaneously, due to a power surge, mechanical failure, or controller card failure or a plethora of other events, the logical volumes will be "lost" along with access to the data. Due to the nature of the RAID 5, all of the drives contain a parody or copy of the original array on one third of its available space. This is what allows a rebuild if only one drive fails. This is the most critical point in safely managing a RAID data recovery as the technician in charge has to decide what to do in case of a 2 or more drive failure. Since the data is no doubt extremely sensitive and expensive his or her job likely depends on what they do next.

If Your RAID 5 Drops 2 or More Disks

If your RAID has a physical or logical malfunction some controller cards will error and force a drop of a second disk which will cause a complete failure of the array. It is unusual, but not unheard of, for 2 drives to fail at the same time. Whatever the cause of the failure you will find that you have no access to the logical volume and if the OS was contained on that it will no longer even boot. You will have to decide if:

• Is the Data Worth Recovering?
• Is There a Backup?
• Can you Replace the Data from Hardcopy?
• Is Data Recovery an Option or a Requirement?

Take Inventory of Your Data

Most commercially used arrays are in service for a particular reason, storing essential data of an exact sort, so you will probably know immediately what was lost. However, if the RAID was a file server, there may be duplicate files on PC’s connected to it. Take a look at the server logs if you are unsure, but make sure that you test the files for date, functionality, and content before restoring them to your file server.

If you have no backups, no duplicates, and no hard copies and the data is simply considered “irreplaceable”, then it is probably worth recovery or at the very least it can be evaluated by a data recovery service for recovery viability. Be sure that the data recovery company gives you a FIRM cost of the evaluation and do some research into the service before you pick the first company name that pops up on your search query.

Are There Hardcopies to Manually Restore From?

You may have all the data that was on the file server stored in paper form and it can be re-entered using your employees or by hiring an outside service for data entry. You must consider this carefully against the option of data recovery. Check the time to re-enter using man hours versus the time of the companies estimate on file recovery to see which is greater. Data recovery can often save thousands of dollars in man hours, but if you had an old backup, 3 or 4 months, then check the cost of restoring it manually. It may be cheaper to have it updated quicker than recovery time depending on the quote for recovery and what your employees are paid.

Be Sure Your Backup is Viable

If you do have a backup be sure to test the files first. Just because you have a backup does not mean that the files you lost are stored in it and that they are functional and current. Many backup software options include choosing what you want to back up and if it was set up incorrectly then the data you lost may not even be present in it. If you found the files you need check them on another system for date of creation and content to be sure that they are, indeed, what you need. If your installed backup software was set to auto save the data it may have been set up incorrectly and what you think was current may be several months old.

Is Data Recovery What You Need?

After taking all these steps into consideration you may still find that you have no way to replace, recreate, or restore the data you lost. If this is the case, then the only choices left are to move on without the data, which may not be a feasible option, or having an experienced data recovery technician attempt a recovery. In most cases if the disks are managed correctly and sent to a reputable firm, the data can be recovered in short order and you will be back up and running in no time.

Source: http://www.datarecoveryaid.com/raid_data_recovery.htm

Source: Chris Gurley- Data Recovery Aid, Inc - Owner/Operator