Overview
The IBM V7000 has 2 types of replication Global Mirror (Asynchronous Replication) and Metro Mirror (Synchronous Replication), both of these type of replication can only be done through the Fibre Channel for block data, the Unified version may be different but I haven't used it.
I am running Firmware version 6.4.1 so the information here is relevant to that version other version may be different. More information can be found on the IBM Info Centre
I am running Firmware version 6.4.1 so the information here is relevant to that version other version may be different. More information can be found on the IBM Info Centre
Global Mirror
The Global Mirror Copy Service provides an asynchronous copy, which means that the secondary volume is not an exact match of the primary volume at every point in time.
This feature is comparable to a continuous backup process in which the last few updates are always missing. When you use Global Mirror for disaster recovery, you must consider how you want to handle these missing updates.
If I/O operations on the primary volume are paused for a small length of time, the secondary volume can become an exact match of the primary volume.
Metro Mirror
Metro Mirror is a type of remote copy that creates a synchronous copy of data from a primary volume to a secondary volume. A secondary volume can either be located on the same system or on another system.
With synchronous copies, host applications write to the primary volume but do not receive confirmation that the write operation has completed until the data is written to the secondary volume. This ensures that both the volumes have identical data when the copy operation completes. After the initial copy operation completes, the Metro Mirror function maintains a fully synchronized copy of the source data at the target site at all times.
The Metro Mirror function supports copy operations between volumes that are separated by distances up to 300 km. For disaster recovery purposes, Metro Mirror provides the simplest way to maintain an identical copy on both the primary and secondary volumes. However, like with all synchronous copies over remote distances, there can be a performance impact to host applications. This performance impact is related to the distance between primary and secondary volumes and depending on application requirements, its use might be limited based on the distance between sites.
The global and metro mirror information above has come from the IBM infocentre, to add to this you can replicate over an IP point to point connection using Global Mirror but this require FCIP Gateway's (Fibre Channel to IP Router), I am replicating between 2 sites using a 1Gbs National Ethernet Circuit which has a latency of ~11ms, Global Mirror should be able to handle up to 80ms latency.
The devices I am using for this are the IBM SAN06B-R which are brocade 7800, I am using 2 at each site for redundancy you can do this with 1 at each site which makes the configuration less complicated.
Once the SAN Fabric has been extended across sites you can configure the replication in the following way. Details oh how to extend fabric can be found here
Problems Encountered
Replication stopping due to Fabric Problems Event ID --- I will find and update---
I went round the houses with this particular problem, it turned out to be down to a faulty SAN06B-R which was appearing to still work but not completely this was identified by IBM support after several sets of logs were sent over. After this device was swapped out all is well.
I have some DB backups running which are sved onto a different volume and the amount of change is too much for the 1Gbs point to point to handle and if left to its own device replication will stop as the link gets saturated. This was resolved by writing 2 scripts which are ran by crontab on a linux server within the environment one script stops the replication consistancy group before the backup runs and the other script restarts the replication consitency group. A tip to find out what commands to run on the command line is the following.
1. log into Storwize V7000 Storage mangement
2. On the left hand side click on the icon that looks like
3. A menu like this should appear
4. click on Remote Copy the following should appear
5. You can expand the consistency group by clicking on the
6. The following should appear
7. click on the consistency group you want to work with then select from the top bar Actions.
8. The following should appear
9. Select the operation you would like to do the following will appear
10. click on the Action in this case Stop Consistency Group, and the following will appear
11. Click on details and you will see the extra information, including the command that can be run on the command line in blue
This can be done for all process to see what command you would need to run at command line.
5. You can expand the consistency group by clicking on the
6. The following should appear
7. click on the consistency group you want to work with then select from the top bar Actions.
8. The following should appear
10. click on the Action in this case Stop Consistency Group, and the following will appear
11. Click on details and you will see the extra information, including the command that can be run on the command line in blue
This can be done for all process to see what command you would need to run at command line.
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