Array-based replication
Array-based replication requires a central data storage unit (SAN or NAS) and a partner unit. With array-based replication, the SAN or NAS processes the data and the commands to process and validate the data being replicated.Advantages of array-based replication
- The work is offloaded from the servers to the storage device.
- You only need one location to control many replications of multiple servers.
- Hosts (Servers) are not required at the second site or to be attached to the second SAN/NAS.
- A central SQL server can be set up to replicate with the servers that actually present applications to users, such as order tracking applications.
- The right software can queue databases to ensure that transactions and the database are in a recoverable state.
Disadvantages of array-based replication
- Cost per device can be high, especially when you’re not replicating all of the data on the SAN.
- Only SAN or NAS based data can be replicated or controlled.
- A second SAN or NAS is required, increasing the cost for the solution.
- There could be compatibility problems of replication technology/software between SAN/NAS hardware and vendors.
Examples of array-based replication software
- HP StorageWorks XP
- EMC SANCOPY - Supports EMC and some other vendor arrays
- EMC MirrorView - EMC only replication
- NetApp SnapMirror
The first method we’ll look at is host-based replication. Simply put, host-based replication is replicating data and using the servers that hold or receive the data to do the work of moving the data. Host-based replication has many advantages.
Advantages of host-based replication
- When you have a small number of servers that require data replication, you can tailor the host-based solution to meet your needs. Customization is key, since you can choose specifically what data to replicate between hosts.
- You can make purchases as needed and phase hosts into the replication strategy.
- You can pick and choose the data that is to be replicated (the entire server doesn’t have to be replicated).
- You can create a schedule for sending data. Depending on the software you’re using, you can throttle bandwidth based on availability and use (i.e., you can increase it in the evenings when the WAN use is less).
- Some solutions allow you to do a many-to-one sender/receiver replication.
- You can have dissimilar storage solutions at each end (Local storage to SAN or NAS, etc.).
Disadvantages of host-based replication
Here are a few disadvantages to using host-based replication:- It requires a sender and receiver to be active on each end. This means that hardware and an OS (and possibly other applications) are required and increase your budget.
- Both the sender and receiver hosts must have the same patch levels for the OS and applications in order to do a true recovery in times of failure.
- With the numbers of servers replicating increases, so does their management time.
- Not all applications can support host-based replication.
Examples of replication software
Here are a couple of replication software packages that are currently available:Network-based replication
The last type of replication is network (or fabric) based replication. This type of replication works separately from the hosts (servers) and the storage devices. A device on the network intercepts packets being sent to and from hosts and arrays and copies them. These copies are replicated to a second device that then replays the packets at a second location. The devices are, in essence, splitters. The data goes in and then it’s split out to different sources.Advantages of network-based replication
- It’s a separate component from the SAN/NAS or the hosts.
- Processing is independent to the host and SAN/NAS.
- It allows replication between multi-vendor products.
Disadvantages of network-based replication
- The cost of implementing devices to support this kind of replication is high.
- Newer technology for the data center, standards, and process are still being worked out.
- There are a limited number of “players” in this area of replication.
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