HP Smart Array 6400 Series Controllers User Guide
RAID 1+0 configurations can tolerate multiple drive failures as long as no
failed drives are mirrored to one another.
RAID 5 configurations can tolerate one drive failure.
RAID ADG configurations can tolerate simultaneous failure of two drives.
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 (refer to "Recovering from
compromised fault tolerance" on page 42).
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. Instead, if the screen displays unrecoverable
error messages, perform the following procedure to recover data:
1. Power down the entire system, and then power it back up. In some cases, a
marginal drive will work again for long enough to enable you to make copies
of important files.
If a 1779 POST message is displayed, press the F2 key to re-enable the
logical volumes. Remember that data loss has probably occurred and any
data on the logical volume is suspect.
2. Make copies of important data, if possible.