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|Clustered KBX5000 replication configuration:|
This is a typical configuration for a clustered implementation of Kashya's KBX5000 replication appliances. These out-of-band appliances can dynamically switch between synchronous and asynchronous replication to respond to application demands.
KBX5000 vs. other techniques
When it comes to IP storage replication, there's no shortage of products. There are array-to-array applications such as EMC's SRDF and HDS' TrueCopy, and host-based products like Veritas Volume Replicator (VVR). An array-based solution suggests like equipment at both sites. Additionally, implementation of synchronous writes when replicating across great distances can affect application performance. While VVR offers a more cost-effective approach than array-based replication, the amount of resources "stolen" from other production processes running on the host will constantly need to be budgeted and revised according to the data growth and availability of the server. The KBX5000, on the other hand, scales independently of the amount of storage per server and doesn't require installing agents on the managed hosts in the consistency group.
And because the KBX5000 doesn't "touch" the array or install host-based agents in the local SAN, license management is limited to the KBX5000 itself, with costs dependent on the amount of storage being replicated. Array- and host-based replication products are typically priced on a per-unit basis in addition to the amount of data replicated.
It should be noted that a Kashya driver needs to be installed on every host whose volumes are replicated. The driver intercepts the write and then sends one copy to the KBX5000 for replication and the other to the source volume.
Better price, performance
All of this adds up to the KBX5000 offering better price performance than array-based, long-distance replication, while being competitive with the more resource-intensive, host-based products.
For example, to replicate 10TB of data using four KBX5000s with the unlimited snapshot and bandwidth-reduction options and a three-year software maintenance agreement (WAN and SAN infrastructure costs are not included), the cost breakdown is as follows:
- Four KBX5000 appliances: $25,500
- Two base licenses (for up to 2TB): $28,800
- Two unlimited snapshots option: $24,000
- Bandwidth-reduction option: $12,000
- Three-year software maintenance: $26,730
- Implementation services: $2,500
The KBX5000 is a non-disruptive, out-of-band replication application that, by dint of its large buffers, doesn't impede the performance of synchronous writes. This promotes application response time and user productivity, but there's still a chance that resynching might be required and a small potential for data loss if the buffer is not supported by battery backup.
By allowing the appliance to profile WAN traffic at the application level and to dynamically switch between synchronous and asynchronous replication policies, Kashya lets applications share the IP WAN pipe without one of them squeezing out another whose traffic is more "bursty" in nature.
But perhaps the biggest benefit the KBX5000 provides is its support of heterogeneous hosts, switches and storage. Because KBX5000 integration happens in the SAN fabric, any nodes that have successfully performed fabric login can be discovered and managed in a consistency group. This is almost always a superior approach to array- and host-based solutions.
This was first published in December 2004