210
EMC Symmetrix DMX-3 Product Guide
Data Integrity, Availability, and Protection
One member rebuild In a one member rebuild, the data members rebuild like RAID 5, the
horizontal parity rebuilds like RAID 5, and diagonal parity rebuilds
using data from all data members.
Two member rebuild In a two data member rebuild, the rebuild is segment by segment
recursively using both horizontal and diagonal parities. In a one data
member and horizontal parity rebuild, the data member is rebuilt using
diagonal parity. The horizontal parity is rebuilt using all data
members.
In a one data member and diagonal parity rebuild, the data member is
rebuilt using horizontal parity. The diagonal parity is rebuilt using all
data members.
In a horizontal parity and diagonal parity rebuild, both horizontal and
diagonal parity is rebuilt using all data member data.
RAID 6 configuration
guidelines
The following are some guidelines to consider when configuring
RAID 6 devices:
â—† BCVs can be RAID 6 devices.
â—† SymmOptimizer Swap supports RAID 6 devices.
â—† SRDF devices can be RAID 6 devices.
â—† eSNAP source and destination devices can be RAID 6 devices.
â—† A log device can be a RAID 6 device.
â—† Concurrent Copy is supported with RAID 6.
Comparing RAID 5
and RAID 6
Table 30 on page 210 describes the comparisons between RAID 5 and
RAID 6.
Table 30 RAID 5 and RAID 6 comparison
RAID 5 RAID 6
Uses two mirrors to represent the device: data mirror and parity
mirror.
Uses a single mirror to represent the overall state of the device.
Uses mirror invalid to indicate both logical and physical invalids. Uses mirror invalid to indicate logical invalid; uses the Physical
Consistency table to indicate physical inconsistent.
Supports both permanent sparing and dynamic sparing. Supports permanent sparing. If permanent sparing is not
successful on the first failure, no additional action is taken. If
permanent sparing is also unsuccessful after a second failure
(double-degraded mode), then RAID 6 dynamic sparing will be
attempted.
Uses special disk commands to perform XOR operations. Uses Symmetrix hardware functionality to perform XOR
calculations.
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