| PRIMECLUSTER Global Disk Services Configuration and Administration Guide 4.1 (Solaris(TM) Operating System) |
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| Appendix A General Notes | > A.2 Important Points |
GDS Snapshot performs copying between the master and the proxy without imposing loads on primary servers or a SAN, by working in cooperation with Advanced Copy functions (EC, OPC) of ETERNUS6000 series, ETERNUS3000 series, and GR700 series disk arrays.
When the Advanced Copy function is available, it is used for copying between the master and the proxy. However, in the following situations, a soft copy function (a copy function of a GDS driver operating on a server) is used.
The Advanced Copy function is not used when:
Use of soft copy functions was specified explicitly using the sdxproxy command with the -e softcopy option
The master and the proxy belong to a root class.
The copy destination volumes are in a mirroring configuration.
Note, however, that even if the master as the copy destination is in a mirroring configuration, OPC is available for copying from the proxy when:
Executing [Operation]:[Proxy Operation]:[Restore] in GDS Management View and selecting "No" to "Rejoin" in the [Restore Master] dialog box. For details see "Restore."
Executing the sdxproxy Restore command. For details see "sdxproxy - Proxy object operations."
A lower level group is connected to a group to which master volumes or proxy volumes belong.
The number of concurrent EC or OPC sessions has reached the upper limit defined by the disk array unit.
The number of allowed concurrent sessions is either the upper limit within one physical disk (LU) or the upper limit within one disk array unit. For details see the handbook of the relevant disk array.
For details on the upper limit of supported concurrent sessions, see the disk array device handbook.
Multiple proxy volumes are related to a master volume and the number of proxy volumes with EC sessions has reached the upper limit (16 volumes).
Disks that constitute the master or the proxy were registered with a class before installing the Advanced Copy function on the disk array unit.
Disks that constitute the master or the proxy were registered with a class before installing GDS Snapshot.
In these situations, operations based on OPC functions are impossible. For such operations see "Instant Snapshot by OPC."
EC is used for synchronization copying from a master to a proxy after joining or rejoining them, copying for maintaining synchronization, and recording the portion updated while a master and a proxy are parted.
OPC is used for synchronization copying, instant snapshot processing, and restoring a master using the proxy data.
If any EC sessions exist between a master and a proxy, OPC cannot be initiated between the master and another proxy.
When both EC and OPC is available as with ETERNUS6000 series, EC has precedence over OPC. Once an EC session is stopped, you cannot use the EC function afterwards. EC sessions are stopped in the following situations.
EC sessions are stopped when:
Executing [Operation]:[Proxy Operation]:[Part] in GDS Management View and selecting "Yes" to "Instant Snapshot" in the [Part Proxy] dialog box
Executing [Operation]:[Proxy Operation]:[Update] in GDS Management View
Executing [Operation]:[Proxy Operation]:[Restore] in GDS Management View
Canceling the EC sessions with the sdxproxy Cancel command
Joining a master and a proxy and using a soft copy function with the sdxproxy Join -e softcopy command
Creating instant snapshots with the sdxproxy Part -e instant command
Rejoining a master and a proxy and using a soft copy function with the sdxproxy Rejoin -e softcopy command
Updating a proxy with the sdxproxy Update command
Restoring master data back from a proxy with the sdxproxy Restore command
To make the EC function available after conducting these operations, break the relationship between the master and the proxy once and rejoin them.
To check the modes of the copying in execution, use either:
The [Copy Type] field of the slice information field in GDS Management View
The CPTYPE field displayed with the sdxinfo command
Additionally, the types and the statuses of sessions between the master and the proxy can be viewed in the FUNC field and the CPSTAT field displayed with the sdxinfo command.
Advanced Copy Control
When the Advanced Copy function is available, executing the sdxproxy command directs GDS to control the Advanced Copy on the master and the proxy. Do not use any other methods other than the sdxproxy command to apply such control on a master and a proxy.
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