According to Chris Lake, corporate IT manager of Sundt Construction, the new WAN optimisation features have already...
saved him some $40,000 a year, but not on bandwidth -- he chalks up that cost savings to the fact that the company has been able to dump the licensing and maintenance on the Double-Take software it was using to replicate data between its headquarters and another site 120 miles away.
Lake said the way Compellent performs replication is also saving him time in the event of a disaster. Most of the company's servers are diskless, he said; the company has several "dark boxes" at the remote site -- Novell servers ready to come to life in the event of a failure at the primary site. The SQL boot volumes and page file are kept at the ready on the SAN rather than requiring the rebuilding of a server at the disaster recovery site in the event of a failure.
"It would take an experienced Novell engineer 8-12 hours to rebuild a box from scratch, Lake said. "By booting off the SAN, we can have the dark box up in 15 minutes."
But, this means that Sundt's disaster recovery plan depends heavily on the SAN at the disaster recovery site being reasonably up-to-date in the event of an outage, especially for the SQL data the company has set to replicate once an hour.
"We estimate that we can get by only if the SQL data is no more than two hours behind," Lake said. This is where quality of service comes in, he said -- by being able to tell the system to prioritise the replication of the SQL data above all others, in order to make sure it's updated most frequently. Meanwhile, Lake said, he's also used the StorageCenter SAN version 3.5 WAN throttling feature to use more bandwidth for backing up less-critical systems like email and file systems across the WAN during off-peak hours and weekends.
Finally, Lake said, he appreciates that the replication software uses web-based GUIs and wizards to guide him through setting replication schedules and QoS parameters.
The new asynchronous replication feature is something Compellent has dubbed "thin replication" -- a combination of deduplication performed before data is sent across the WAN, and another process based on the array's thin provisioning feature.
As with thin provisioning -- in which space is not allocated for data until it's actually written -- Compellent's updated software sends only changed packets over the WAN rather than replicating volume-to-volume on an identical array at the other end of the wire. This means it doesn't send empty blocks or require the preallocation of space on the other end of the wire for data.
"It is very positive to see this kind of replication capability being baked into storage [software], especially for medium and small deployments," said Brad O'Neill, senior analyst with the Taneja Group. "There is a clear trend [among] the emerging systems suppliers requiring them to bring advanced software features into their offering right out of the gate -- it's the only way to [present themselves as] a viable alternative to the big guys."
Compellent is not alone in offering baked-in replication -- its midrange rival EqualLogic also has the feature, though EqualLogic's replication software does not include the optimisation piece.
"Replicated data from our arrays can be handled in whatever QoS class the network…managers decide," wrote Dylan Locsin, public relations manager for EqualLogic, in an email to SearchStorage. "This provides a consistent single method for managing QoS in the network for the entire organization."
The features finding their way into midrange arrays could be a boon to the right users, according to O'Neill, but these products will probably only continue to appeal to small or midsized companies with homogeneous environments. Larger, more complex environments with a combination of host, network and array-based replication will probably not find the product useful, he said.