Lenovo ThinkServer RD240 MegaRAID SAS Software User Guide - Page 59

RAID Configuration Strategies, RAID 60 Level Virtual Drive, Table 2.12

Page 59 highlights

Table 2.12 RAID 60 Overview Weak Points Drives Not well suited to tasks requiring lot of writes. A RAID 60 virtual drive has to generate two sets of parity data for each write operation, which results in a significant decrease in performance during writes. Drive performance is reduced during a drive rebuild. Environments with few processes do not perform as well because the RAID overhead is not offset by the performance gains in handling simultaneous processes. RAID 6 costs more because of the extra capacity required by using two parity blocks per stripe. A minimum of 8 Figure 2.12 shows a RAID 6 data layout. The second set of parity drives are denoted by Q. The P drives follow the RAID 5 parity scheme. Figure 2.12 RAID 60 Level Virtual Drive RAID 60 Segment 1 Segment 8 Parity (Q11-Q12) Parity (P15-P16) Segment 2 Parity (Q3-Q4) Parity (P11-P12) Segment 15 Parity (Q1-Q2) Parity (P3-P4) Segment 11 Segment 16 Parity (P1-P2) Segment 7 Segment 12 Parity (Q15-Q16) Segment 3 Segment 6 Parity (Q9-Q10) Parity (P13-P14) Segment 4 Parity (Q5-Q6) Parity (P9-P10) Segment 13 Parity (Q3-Q4) Parity (P5-P6) Segment 9 Segment 14 Parity (P3-P4) Segment 5 Segment 10 Parity (Q13-Q14) RAID 6 RAID 0 Note: Parity is distributed across all drives in the drive group. RAID 6 2.6 RAID Configuration Strategies The most important factors in RAID drive group configuration are: • Virtual drive availability (fault tolerance) • Virtual drive performance • Virtual drive capacity You cannot configure a virtual drive that optimizes all three factors, but it is easy to choose a virtual drive configuration that maximizes one factor at the expense of another factor. For example, RAID 1 (mirroring) provides excellent fault tolerance, but requires a redundant drive. The following subsections describe how to use the RAID levels to RAID Configuration Strategies 2-27

  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10
  • 11
  • 12
  • 13
  • 14
  • 15
  • 16
  • 17
  • 18
  • 19
  • 20
  • 21
  • 22
  • 23
  • 24
  • 25
  • 26
  • 27
  • 28
  • 29
  • 30
  • 31
  • 32
  • 33
  • 34
  • 35
  • 36
  • 37
  • 38
  • 39
  • 40
  • 41
  • 42
  • 43
  • 44
  • 45
  • 46
  • 47
  • 48
  • 49
  • 50
  • 51
  • 52
  • 53
  • 54
  • 55
  • 56
  • 57
  • 58
  • 59
  • 60
  • 61
  • 62
  • 63
  • 64
  • 65
  • 66
  • 67
  • 68
  • 69
  • 70
  • 71
  • 72
  • 73
  • 74
  • 75
  • 76
  • 77
  • 78
  • 79
  • 80
  • 81
  • 82
  • 83
  • 84
  • 85
  • 86
  • 87
  • 88
  • 89
  • 90
  • 91
  • 92
  • 93
  • 94
  • 95
  • 96
  • 97
  • 98
  • 99
  • 100
  • 101
  • 102
  • 103
  • 104
  • 105
  • 106
  • 107
  • 108
  • 109
  • 110
  • 111
  • 112
  • 113
  • 114
  • 115
  • 116
  • 117
  • 118
  • 119
  • 120
  • 121
  • 122
  • 123
  • 124
  • 125
  • 126
  • 127
  • 128
  • 129
  • 130
  • 131
  • 132
  • 133
  • 134
  • 135
  • 136
  • 137
  • 138
  • 139
  • 140
  • 141
  • 142
  • 143
  • 144
  • 145
  • 146
  • 147
  • 148
  • 149
  • 150
  • 151
  • 152
  • 153
  • 154
  • 155
  • 156
  • 157
  • 158
  • 159
  • 160
  • 161
  • 162
  • 163
  • 164
  • 165
  • 166
  • 167
  • 168
  • 169
  • 170
  • 171
  • 172
  • 173
  • 174
  • 175
  • 176
  • 177
  • 178
  • 179
  • 180
  • 181
  • 182
  • 183
  • 184
  • 185
  • 186
  • 187
  • 188
  • 189
  • 190
  • 191
  • 192
  • 193
  • 194
  • 195
  • 196
  • 197
  • 198
  • 199
  • 200
  • 201
  • 202
  • 203
  • 204
  • 205
  • 206
  • 207
  • 208
  • 209
  • 210
  • 211
  • 212
  • 213
  • 214
  • 215
  • 216
  • 217
  • 218
  • 219
  • 220
  • 221
  • 222
  • 223
  • 224
  • 225
  • 226
  • 227
  • 228
  • 229
  • 230
  • 231
  • 232
  • 233
  • 234
  • 235
  • 236
  • 237
  • 238
  • 239
  • 240
  • 241
  • 242
  • 243
  • 244
  • 245
  • 246
  • 247
  • 248
  • 249
  • 250
  • 251
  • 252
  • 253
  • 254
  • 255
  • 256
  • 257
  • 258
  • 259
  • 260
  • 261
  • 262
  • 263
  • 264
  • 265
  • 266
  • 267
  • 268
  • 269
  • 270
  • 271
  • 272
  • 273
  • 274
  • 275
  • 276
  • 277
  • 278
  • 279
  • 280
  • 281
  • 282
  • 283
  • 284
  • 285
  • 286
  • 287
  • 288
  • 289
  • 290
  • 291
  • 292
  • 293
  • 294
  • 295
  • 296
  • 297
  • 298
  • 299
  • 300
  • 301
  • 302
  • 303
  • 304
  • 305
  • 306
  • 307
  • 308
  • 309
  • 310
  • 311
  • 312
  • 313
  • 314
  • 315
  • 316
  • 317
  • 318
  • 319
  • 320
  • 321
  • 322
  • 323
  • 324
  • 325
  • 326
  • 327
  • 328
  • 329
  • 330
  • 331
  • 332
  • 333
  • 334
  • 335
  • 336
  • 337
  • 338
  • 339
  • 340
  • 341
  • 342
  • 343
  • 344
  • 345
  • 346
  • 347
  • 348
  • 349
  • 350
  • 351
  • 352
  • 353
  • 354
  • 355
  • 356
  • 357
  • 358
  • 359
  • 360
  • 361
  • 362
  • 363
  • 364

RAID Configuration Strategies
2-27
Figure 2.12
shows a RAID 6 data layout. The second set of parity drives
are denoted by
Q
. The
P
drives follow the RAID 5 parity scheme.
Figure 2.12
RAID 60 Level Virtual Drive
2.6
RAID Configuration Strategies
The most important factors in RAID drive group configuration are:
Virtual drive availability (fault tolerance)
Virtual drive performance
Virtual drive capacity
You cannot configure a virtual drive that optimizes all three factors, but it
is easy to choose a virtual drive configuration that maximizes one factor
at the expense of another factor. For example, RAID 1 (mirroring)
provides excellent fault tolerance, but requires a redundant drive.
The following subsections describe how to use the RAID levels to
Weak Points
Not well suited to tasks requiring lot of writes. A RAID
60 virtual drive has to generate two sets of parity data
for each write operation, which results in a significant
decrease in performance during writes. Drive
performance is reduced during a drive rebuild.
Environments with few processes do not perform as
well because the RAID overhead is not offset by the
performance gains in handling simultaneous processes.
RAID 6 costs more because of the extra capacity
required by using two parity blocks per stripe.
Drives
A minimum of 8
Table 2.12
RAID 60 Overview
Segment 1
Segment 8
Segment 2
Segment 7
Segment 10
Segment 5
Parity (P1-P2)
Parity (Q11–Q12)
Note:
Parity is distributed across all drives in the drive group.
Parity (Q1-Q2)
Segment 11
Segment 12
Parity (P15-P16)
Segment 15
Segment 16
Parity (Q15-Q16)
Segment 3
Segment 6
Segment 4
Parity (P9-P10)
Parity (Q9–Q10)
Parity (P11-P12)
Segment 9
Parity (P13-P14)
Segment 14
Segment 13
Parity (Q13-Q14)
RAID
60
RAID 6
RAID 6
RAID 0
Parity (Q3-Q4)
Parity (P3-P4)
Parity (Q5-Q6)
Parity (P5-P6)
Parity (P3-P4)
Parity (Q3-Q4)