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9.1.3 Administration and management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
9.2 Stretch MetroCluster with SAS shelves and SAS cables . . . . . . . . . . . . . . . . . . . . . . 131
9.2.1 Before you begin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
9.2.2 Installing a new system with SAS disk shelves by using SAS optical cables . . . 133
9.2.3 Replacing SAS cables in a multipath HA configuration. . . . . . . . . . . . . . . . . . . . 135
9.2.4 Hot-adding an SAS disk shelf by using SAS optical cables . . . . . . . . . . . . . . . . 137
9.2.5 Replacing FibreBridge and SAS copper cables with SAS optical cables . . . . . . 141
Chapter 10. Data protection with RAID Double Parity . . . . . . . . . . . . . . . . . . . . . . . . . 147
10.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
10.2 Why use RAID-DP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
10.2.1 Single-parity RAID using larger disks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
10.2.2 Advantages of RAID-DP data protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
10.3 RAID-DP overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
10.3.1 Protection levels with RAID-DP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
10.3.2 Larger versus smaller RAID groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
10.4 RAID-DP and double parity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
10.4.1 Internal structure of RAID-DP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
10.4.2 RAID 4 horizontal row parity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
10.4.3 Adding RAID-DP double-parity stripes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
10.4.4 RAID-DP reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
10.4.5 Protection levels with RAID-DP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
10.5 Hot spare disks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
Chapter 11. Core technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
11.1 Write Anywhere File Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
11.2 Disk structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
11.3 NVRAM and system memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
11.4 Intelligent caching of write requests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
11.4.1 Journaling write requests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
11.4.2 NVRAM operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
11.5 N series read caching techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
11.5.1 Introduction of read caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
11.5.2 Read caching in system memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
Chapter 12. Flash Cache. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
12.1 About Flash Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
12.2 Flash Cache module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
12.3 How Flash Cache works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
12.3.1 Data ONTAP disk read operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
12.3.2 Data ONTAP clearing space in the system memory for more data . . . . . . . . . 177
12.3.3 Saving useful data in Flash Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
12.3.4 Reading data from Flash Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
Chapter 13. Disk sanitization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
13.1 Data ONTAP disk sanitization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
13.2 Data confidentiality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
13.2.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
13.2.2 Data erasure and standards compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
13.2.3 Technology drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
13.2.4 Costs and risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
13.3 Data ONTAP sanitization operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
13.4 Disk Sanitization with encrypted disks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
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