You can create GAD pairs without using an external storage system, if you do not set a volume for the quorum disk.
In this configuration, I/Os from the server might stop if a failure occurs in a path or a storage system. Therefore, determine whether to set a volume using an external volume for the quorum disk or not according to the requirements of your planned usage. The following figure illustrates the configuration without a volume set for the quorum disk.
The GAD configuration without a volume set for the quorum disk supports migrating data for the following:
- From a VSP G1x00 storage system to another VSP G1x00.
- From a VSP G200, G/F400, G/F600, or G/F800 storage system to a VSP 5000 series.
- From a VSP G1x00 or F1500 storage system to a VSP G/F350, G/F370, G/F700, G/F900.
- From a VSP G200, G/F400, G/F600, or G/F800 storage system to a VSP G/F350, G/F370, G/F700, G/F900.
- From a VSP G/F350, G/F370, G/F700, G/F900 storage system to another VSP G/F350, G/F370, G/F700, G/F900.
- From a VSP E series storage system to another VSP E series
When you do not set a volume for a quorum disk, you do not need the following components and steps:
- External storage system
- External port between storage systems (A) and (B)
- Path and a switch between storage system (A) and the external storage system
- Path and a switch between storage system (B) and the external storage system
The following describes the differences between the configuration with a volume set for the quorum disk and the configuration without a volume set for the quorum disk.
As shown in the following figure and table, if a failure occurs in the primary storage system when an external storage system is not used for the quorum disk, the process stops. Because this failure can occur, you should use the configuration that does not set volumes for the quorum disk temporarily for migrating data (VSP E series and VSP G/F350, G/F370, G/F700, G/F900). If the process is not allowed to stop due to a failure in the primary storage system, create a configuration with a volume set for the quorum disk (VSP 5000 series and VSP G1x00, or F1500 ).
The figure shows failure points and the table describes whether the process stops or not according to the location in which the failure occurred.
| Number in the figure | Failure location | Operation | |
|---|---|---|---|
| With volumes set for quorum disks | Without volumes set for quorum disks | ||
| 1 | Primary storage system | Continues | Stops |
| 2 | Secondary storage system | Continues | Continues |
| 3 | External storage system | Continues | Not applicable |
| 4 | Primary volume | Continues | Continues |
| 5 | Secondary volume | Continues | Continues |
| 6 | Quorum disk | Continues | Not applicable |
| 7 | Remote path from the primary storage system to the secondary storage system | Continues | Continues |
| 8 | Remote path from the secondary storage system to the primary storage system | Continues | Continues |
| 9 | Path between the primary storage system and the quorum disk | Continues | Not applicable |
| 10 | Path between the secondary storage system and the quorum disk | Continues | Not applicable |
| 11 | When the failures occur at the same time in the following locations:
|
Continues | Continues |
| 12 | When the failures occur at the same time in the following locations:
|
Stops | Not applicable |
Cost
A second difference between the configuration with a volume set for the quorum disk and the configuration without a volume set for the quorum disk is cost. If you do not set a volume for the quorum disk, you can save the preparation cost because you do not need an external storage system and the path. Also, some steps for configuring the GAD environment are not necessary.