HP StorageWorks SB40c HP StorageWorks SB40c Storage Blade User Guide (433904-0 - Page 23

Compromised fault tolerance If more hard drives fail than the fault-tolerance method allows, fault tolerance is compromised, and the logical drive fails. In this case, all requests from the operating system are rejected with unrecoverable errors. You are likely to lose data, although it can sometimes be recovered. One example of a situation in which compromised fault tolerance may occur is when a drive in an array fails while another drive in the array is being rebuilt. If the array has no online spare, any logical drives in this array that are configured with RAID 5 fault tolerance will fail. Compromised fault tolerance can also be caused by non-drive problems, such as a faulty cable or temporary power loss to a storage system. In such cases, you do not need to replace the physical drives. However, you may still have lost data, especially if the system was busy at the time that the problem occurred. Recovering from compromised fault tolerance If fault tolerance is compromised, inserting replacement drives does not improve the condition of the logical volume. Perform the following procedure to recover data: 1. Power down the SB40c ("Power down" on page 9). 2. Power up the SB40c ("Power up" on page 9). In some cases, a marginal drive is operational long enough to allow backup of important files. 3. Make copies of important data, if possible. 4. Replace any failed drives. Factors to consider before replacing hard drives Be sure that the server blade is the first unit to be powered down and the last to be powered back up. Taking this precaution ensures that the system does not erroneously mark the drives as failed when the server blade is powered up. Before replacing a degraded drive: • Open HP SIM and inspect the Error Counter window for each physical drive in the same array to confirm that no other drives have any errors. (For details, refer to the HP SIM documentation on the Management CD.) • Be sure that the array has a current, valid backup. • Use replacement drives that have a capacity at least as great as that of the smallest drive in the array. The controller immediately fails drives that have insufficient capacity. To minimize the likelihood of fatal system errors, take these precautions when removing failed drives: • Do not remove a degraded drive if any other drive in the array is offline (the online LED is off). In this situation, no other drive in the array can be removed without data loss. Exceptions: o When RAID 1+0 is used, drives are mirrored in pairs. Several drives can be in a failed condition simultaneously (and they can all be replaced simultaneously) without data loss, as long as no two failed drives belong to the same mirrored pair. o When RAID 6 is used, two drives can fail simultaneously (and be replaced simultaneously) without data loss. o If the offline drive is a spare, the degraded drive can be replaced. Troubleshooting 23