Compromised Fault Tolerance; Recovering From Compromised Fault Tolerance (Enabling Failed Luns) - HP AD510A - StorageWorks Modular Smart Array 1500 cs 2U Fibre Channel SAN Attach Controller Shelf Hard Drive Maintenance And Service Manual

• RAID 6 configurations can tolerate simultaneous failure of two hard drives in the array.

Compromised fault tolerance

Each RAID configuration has inherent limitations on the number of physical hard drive failures that it can
tolerate. If more hard drives fail than the fault-tolerance method allows, fault tolerance is compromised.
When the MSA determines that the fault tolerance of a LUN is compromised, the LUN is taken offline
and subsequent I/O requests are rejected. This is designed to protect the integrity of the LUN, but does
require manual intervention to recover or re-enable the LUN. You are likely to lose data, although it
can sometimes be recovered.
Common causes of compromised fault tolerance include:
• More hard drives fail than the LUN can tolerate.
For example, in a RAID 5 array, if a hard 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.
• A SCSI cable could be broken or disconnected.
• A temporary loss of power.
For example, if both power supplies are inappropriately connected to the same power source and that
power source it interrupted, fault tolerance may be compromised.
Recovering from compromised fault tolerance (enabling failed
LUNs)
If fault tolerance is compromised, inserting replacement hard drives does not improve the condition of the
logical unit. The procedure to re-enable or accept a LUN that is unresponsive is performed in the Array
Configuration Utility (ACU) or the MSA Command Line Interface (MSA-CLI).
1.
Stop all I/O activity.
2.
Turn off the system as described in
3. Check for loose, dirty, broken, or bent cabling and connectors on all devices.
4.
Remove and then reinsert all hard drives and controllers.
CAUTION:
Data can be lost if the hard drives are not firmly reseated.
5. Turn the system on as described in
NOTE:
In some cases, a marginal hard drive might work again for long enough to allow you
to make copies of important files.
6. If using the MSA LCD panel:
a. If one of the following messages are displayed on the MSA array controller LCD front panel, an
issue was found with one or more configured LUNs that may result in data loss, so all of the
hard drives in the LUNs have been disabled. Press the right push button to re-enable the LUNs.
02 ENABLE VOLUME <n>?
04 ENABLE VOLUMES ? '<'=NO, '>'=YES
98
Hard drive failures and faulted LUNs
Removing power from the
Applying power to the MSA.
'<'=NO, '>'=YES
MSA.