Fast Recovery; Figure 15 Fast Recovery - Fujitsu ETERNUS AF250 Design Manual

1. Function
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 AF) 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 si-
multaneously.

Figure 15 Fast Recovery

RAID6-FR (No redundancy)
RAID6-FR (Redundant)
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)
FUJITSU Storage ETERNUS AF250 S2, ETERNUS AF250 All-Flash Arrays Design Guide (Basic)
Copyright 2019 FUJITSU LIMITED
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
33
: Redundant data for area A
of the failed drive
: Redundant data for area B
of the failed drive
: Fast recovery Hot Spare (FHS)
P3AG-1822-09ENZ0