Disk Rebuilds; Rebuild Rate - Lenovo ThinkServer RD650 User Manual

12Gb/s MegaRAID SAS Software User Guide
March 2014
Hot spare drives can be located on any RAID channel. Standby hot spares (not being used in RAID drive group) are
polled every 60 seconds at a minimum, and their status made available in the drive group management software.
RAID controllers offer the ability to rebuild with a disk that is in a system but not initially set to be a hot spare.
Observe the following parameters when using hot spares:
Hot spares are used only in drive groups with redundancy: RAID levels 1, 5, 6, 10, 50, and 60.

A hot spare connected to a specific RAID controller can be used to rebuild a drive that is connected only to the

same controller.
You must assign the hot spare to one or more drives through the controller BIOS or use drive group management

software to place it in the hot spare pool.
A hot spare must have free space equal to or greater than the drive it replaces. For example, to replace an 500-GB

drive, the hot spare must be 500-GB or larger.
2.1.13

Disk Rebuilds

When a drive in a RAID drive group fails, you can rebuild the drive by re-creating the data that was stored on the drive
before it failed. The RAID controller re-creates the data using the data stored on the other drives in the drive group.
Rebuilding can be done only in drive groups with data redundancy, which includes RAID 1, 5, 6, 10, 50, and 60 drive
groups.
The RAID controller uses hot spares to rebuild failed drives automatically and transparently, at user-defined rebuild
rates. If a hot spare is available, the rebuild can start automatically when a drive fails. If a hot spare is not available, the
failed drive must be replaced with a new drive so that the data on the failed drive can be rebuilt.
The failed drive is removed from the virtual drive and marked ready awaiting removal when the rebuild to a hot spare
begins. If the system goes down during a rebuild, the RAID controller automatically resumes the rebuild after the
system reboots.
An automatic drive rebuild will not start if you replace a drive during a RAID-level migration. The rebuild must be
started manually after the expansion or migration procedure is complete. (RAID-level migration changes a virtual
drive from one RAID level to another.)
2.1.14

Rebuild Rate

The rebuild rate is the percentage of the compute cycles dedicated to rebuilding failed drives. A rebuild rate of 100
percent means that the system assigns priority to rebuilding the failed drives.
The rebuild rate can be configured between 0 percent and 100 percent. At 0 percent, the rebuild is done only if the
system is not doing anything else. At 100 percent, the rebuild has a higher priority than any other system activity.
Using 0 percent or 100 percent is not recommended. The default rebuild rate is accelerated.
NOTE When the rebuild to a hot spare begins, the failed drive is often
removed from the virtual drive before management applications
detect the failed drive. When this occurs, the events logs show the
drive rebuilding to the hot spare without showing the failed drive. The
formerly failed drive will be marked as "ready" after a rebuild begins to
a hot spare. If a source drive fails during a rebuild to a hot spare, the
rebuild fails, and the failed source drive is marked as offline. In
addition, the rebuilding hot spare drive is changed back to a hot spare.
After a rebuild fails because of a source drive failure, the dedicated hot
spare is still dedicated and assigned to the correct drive group, and the
global hot spare is still global.
LSI Corporation
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Chapter 2: Introduction to RAID
Components and Features