Fast Recovery; Figure 13 Fast Recovery - Fujitsu ETERNUS DX S5 Series Design Manual

2. Basic Functions
Data Protection

Fast Recovery

This function recovers data quickly by relocating data in the failed drive to the other remaining drives when a
drive error is detected.
For a RAID group that is configured with RAID6-FR, Fast Recovery is performed for the reserved area that is
equivalent to hot spares in the RAID group when a drive error occurs.
If a second drive fails when the reserved area is already used by the first failed drive, a normal rebuild (hot spare
rebuild in the ETERNUS DX) is performed.
For data in a failed drive, redundant data and reserved space are allocated in different drives according to the
area. A fast rebuild can be performed because multiple rebuild processes are performed for different areas
simultaneously.
Figure 13 Fast Recovery
RAID6-FR (No redundancy)
RAID6-FR (Redundant)
Caution
For the Fast Recovery function that is performed when the first drive fails, a copyback is performed after
the failed drive is replaced even if the Copybackless function is enabled.
For a normal rebuild process that is performed when the reserved space is already being used and the
second drive fails, a copyback is performed according to the settings of the Copybackless function.
High Speed Rebuilding
(Creating data and writing to the FHS area simultaneously)
Failure
RAID6-FR ((3D+2P) × 2 + 1HS)
Disconnect
RAID6-FR ((3D+2P) × 2)
A failed drive is disconnected from the
ETERNUS storage system.
Data is created from the redundant data
in normal drives and written to reserved
space (FHS) in RAID6-FR.
Failed drive
52
: Redundant data for area A
of the failed drive
: Redundant data for area B
of the failed drive
: Fast recovery Hot Spare (FHS)
Design Guide