User guide

Chapter 9. Maintaining Units
146 3ware Serial ATA RAID Controller User Guide
Background Initialization After Power Failure
The 3ware controller detects and handles power failures, using a mechanism
that ensures that redundant units have consistent data and parity. When a
redundant unit is unexpectedly shutdown, there is a possibility some data and
parity may be inconsistent. If a unit or sub-unit of a redundant unit is detected
to have been shutdown uncleanly, the unit or sub-unit will change its mode to
either ‘Initializing’ or ‘Verifying.’
When the initialization is complete, the unit is guaranteed to be redundant
again. The initialization does not erase user data.
About Verification
The verify feature combines verification of redundant units (confirming the
validity of the redundant data) and media scans for non-redundant units.
Verification can provide early warning of a disk drive problem or failure. This
allows you to replace drives before they fail.
You can manually request a verify, or you can enable the Auto Verify policy,
and the controller will automatically start verification once every 24 hours.
(See “Starting a Verify Manually” on page 148 and “Setting Auto Verify for a
Unit” on page 109.)
During verification, I/O continues normally, but with a slight performance
loss, depending on your verify rate setting. You can adjust how much
verification will slow performance by setting a rate at which it occurs. (See
“Setting Background Task Rate” on page 155.) You can also postpone
verification until a scheduled time. (See “Scheduling Background Tasks” on
page 156.)
Yes RAID 5 with 5 or more disks
RAID 6
RAID 50 with subunits of 5 or more disks
Table 12: Initialization Requirements for Different RAID
Configurations
Initialization Required
for Highest
Performance?
RAID Configurations
Note: Not verifying the unit periodically can lead to an unstable array unit and may
cause data loss.
It is strongly recommended that you schedule a verify at least 1 time per week.