HP Surestore 64 FW 05.01.00 and SW 07.01.00 HP StorageWorks SAN High Availabil - Page 99

ISL Oversubscription, ISL oversubscription, serviced

Page 99 highlights

Planning Considerations for Fibre Channel Topologies Prior to fabric design, application I/O profiles should be estimated or established that classify the application bandwidth requirements. Bandwidth consumption is classified as light, medium, or heavy. These classifications must be considered when planning ISL and device connectivity. For information about application I/O (in Gbps) and fabric performance problems due to ISL connectivity, refer to "ISL Oversubscription." For information about application I/O (in IOPS) and fabric performance problems due to port contention, refer to "Device Fan-Out Ratio" on page 101. ISL Oversubscription ISL oversubscription (or congestion) occurs when multiplexed traffic from several devices is transmitted across a single ISL. When an ISL is oversubscribed, fabric elements use fairness algorithms to interleave data frames from multiple devices, thus giving fractional bandwidth to the affected devices. Although all devices are serviced, ISL and fabric performance is reduced. Figure 41 illustrates ISL oversubscription. Two NT servers, each with maximum I/O of 100 MBps, are contending for the bandwidth of a single ISL operating at 1.0625 Gbps. In addition to data, the ISL must also transmit Class F traffic internal to the fabric. When operating at peak load, each NT server receives less than half the available ISL bandwidth. Storage TM 1 Gbps ISL 200 Bandwidth (MBps) TM 150 100 50 NT Server 1 NT Server 2 (100 MBps Max) (100 MBps Max) 0 15 Figure 41: ISL oversubscription 1 Gbps ISL NT Server 1 NT Server 2 10 15 20 25 Time (Sec) SAN High Availability Planning Guide 99

  • 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

Planning Considerations for Fibre Channel Topologies
99
SAN High Availability Planning Guide
Prior to fabric design, application I/O profiles should be estimated or established
that classify the application bandwidth requirements. Bandwidth consumption is
classified as
light
,
medium
, or
heavy
. These classifications must be considered
when planning ISL and device connectivity. For information about application I/O
(in Gbps) and fabric performance problems due to ISL connectivity, refer to “
ISL
Oversubscription
.” For information about application I/O (in IOPS) and fabric
performance problems due to port contention, refer to “
Device Fan-Out Ratio
on page 101.
ISL Oversubscription
ISL oversubscription (or congestion) occurs when multiplexed traffic from several
devices is transmitted across a single ISL. When an ISL is oversubscribed, fabric
elements use fairness algorithms to interleave data frames from multiple devices,
thus giving fractional bandwidth to the affected devices. Although all devices are
serviced, ISL and fabric performance is reduced.
Figure 41
illustrates ISL oversubscription. Two NT servers, each with maximum
I/O of 100 MBps, are contending for the bandwidth of a single ISL operating at
1.0625 Gbps. In addition to data, the ISL must also transmit Class F traffic
internal to the fabric. When operating at peak load, each NT server receives less
than half the available ISL bandwidth.
Figure 41:
ISL oversubscription
NT Server 1
(100 MBps Max)
1 Gbps ISL
Storage
NT Server 2
(100 MBps Max)
1
5
10
15
20
25
0
100
150
200
Time (Sec)
Bandwid
th (MBp
s)
50
1 Gbps ISL
NT Server 1
NT Server 2