This does actually happen indeed. This is why NetApp storage solutions have an implementation of RAID 6. This is just in case you lose a second drive during the rebuild.

You can calculate the likelihood of a failure using the standard formulas listed on the following page link text As you scale to larger and larger numbers of data drives, the likelihood of just such a failure goes up. If you have enough disks you could push this number into the worry zone if you are using a RAID 5 with a huge number of data volumes.

Hope this helps

This does actually happen indeed. This is why NetApp storage solutions have an implementation of RAID 6. This is just in case you lose a second drive during the rebuild.

You can calculate the likelihood of a failure using the standard formulas listed on the following page link text As you scale to larger and larger numbers of data drives, the likelihood of just such a failure goes up. If you have enough disks you could push this number into the worry zone if you are using a RAID 5 with a huge number of data volumes.

I can tell you from personal experience that you certainly can have two drive failures in the same array within the same critical timeframe. Raid 6 saved me from having to restore from backup.

Hope this helps