Guidelines, Data recovery (rebuild), Time required for a rebuild – HP Dynamic Smart Array Controllers User Manual
Page 22
Replacing, moving, or adding hard drives 22
In RAID 5 configurations, you can replace one failed drive. When a physical drive fails, data that was on the
failed drive can be calculated from the remaining parity data and user data on the other drives in the array.
This recovered data is usually written to an online spare in a process called a rebuild.
Guidelines
Before replacing hard drives, observe the following guidelines:
•
Be sure that the array has a current, valid backup.
•
Confirm that the replacement drive is one of the following:
o
For B120i controllers—SATA or SATA SSD drives
o
For B320i controllers—SATA, SATA SSD, or SAS drives
ACU does not allow mixing SAS and SATA drives in the same array.
•
Use replacement drives that have a capacity equal to or greater than the smallest drive in the array. The
controller immediately fails drives that have insufficient capacity.
•
After removing a drive, wait 3 seconds. After 3 seconds, the firmware generates an event indicating
that the drive has been removed. You can now safely install a new drive.
To replace more drives in an array than the fault tolerance method can support, follow the previous
guidelines for replacing several drives simultaneously. Wait until rebuild is complete, as indicated by
ACU/ACU-CLI, before replacing additional drives.
If you need to replace more drives than the fault tolerance method can support because fault tolerance has
been compromised, back up the data before replacing any drives. For more information, see "Recovering
from compromised fault tolerance (on page
)."
Data recovery (rebuild)
When you replace a hard drive in an array, the controller uses the fault-tolerance information on the
remaining drives in the array to reconstruct the data from the original drive and write it to the replacement
drive. This process is called automatic data recovery or rebuild. If fault tolerance is compromised, this data
cannot be reconstructed and, likely, is lost permanently.
Rebuilding an array requires that you either be in offline ACU or booted into the operating system with the
driver installed.
The operating system must be running for the rebuild to occur.
If another drive in the array fails while fault tolerance is unavailable during rebuild, a fatal system error can
occur, and all data on the array is then lost. In exceptional cases, however, failure of another drive does not
always cause a fatal system error. These exceptions include the following:
•
Failure after activation of a spare drive
•
Failure of a drive that is not mirrored to any other failed drives (in a RAID 1+0 configuration)
Time required for a rebuild
The time required for a rebuild varies, depending on several factors:
•
The priority that the rebuild is given over normal I/O operations
Change the priority setting with ACU ("
" on page