By Michele Hope
—When disk-to-disk (D2D) backup first became part of the storage industry lexicon, a portion of intrepid users volunteered to put the first wave of disk-based backup products through its paces. Still, others decided to wait and see how this emerging technology would ultimately play out.
Since then, many users have successfully incorporated D2D into part—or sometimes all—of their backup routine. Although some users have replaced tape with disk, most have taken more of a middle-ground approach, choosing to use disk as a short-term staging area for backup data that is subsequently streamed to tape.
The following case studies illustrate how some end users are taking advantage of D2D backup/recovery, with an emphasis on some of the new architectures.
De-dupe and compress
Several organizations use D2D systems that offer some type of high compression ratio for backup data. This technology—also known as de-duplication, single-instance storage, or content optimized storage (COS)—typically eliminates the backup of duplicate data by identifying and storing just the block-, byte-, or bit-level changes or additions made to data sets since the prior backup data was saved. As a result, users can back up their data using a fraction of the disk storage they'd otherwise require.
One such user is Paul Scheib, director of IS operations at Children's Hospital in Boston, a non-profit Harvard University teaching hospital and one of the largest pediatric hospitals in the country. For their first foray into disk-based backup, Scheib and his team tried virtual tape library (VTL) technology to address the growing tape hardware issues and errors they had begun to experience when they were attempting to back up 80TB of data from the hospital's estimated 400 Unix and Windows servers.
After less-than-satisfactory results with the VTL, and no significant increase in the speed of backups going to the virtual tape library, Scheib concluded it wasn't so much VTL technology at fault as it was the need for the hospital to overhaul its current backup architecture.
After completing the re-architecting, which involved consolidation to larger media servers, Children's Hospital took a new look at D2D with Data Domain and its claim of 20:1 compression ratios. Scheib figured 20:1 sounded a lot better than the 3:1 compression ratios some VTL solutions had claimed when he first ventured into D2D.
The hospital wanted to save as much as two months of backup data on disk. Compression ratios would play a key role in finding an affordable D2D solution. Needing to back up somewhere between 80TB to 100TB of production data each week (and the two-month equivalent of more than 800TB of traditional backup data), Scheib and his team projected they would need only 50TB of physical disk capacity from within the Data Domain DD400 Enterprise Series. This estimate has since played out, thanks to sustainable data compression ratios across the board of approximately 20:1, which was a surprise to Scheib because he expected more fluctuation in compression ratios for different types of data.
Says Scheib, "When you look at the usable space we get with compression, it comes out to at least half the cost of a Clariion or EVA-class disk array, and probably greater than that. If you buy into getting a 20:1 compression ratio, it's just hard for anything to compete from a price standpoint."
Scheib now has six Data Domain systems plugged into the hospital's Ethernet network, with plans to move them to a secondary location where backup jobs will be subsequently redirected over a WAN. Although his team currently replicates nightly to tape, he looks forward to moving to just monthly tape backup once backups to the secondary location are up and running.
D2D reduces stress
Virgil Vaclavik, technical services manager at oil industry manufacturer Hydril LP, was also impressed with the compression rates he began seeing from his company's recently implemented EVault InfoStage software. The software uses EVault's DeltaPro technology to compress and encrypt backup data prior to sending it to a local or remote "vault" also managed by the customer. It identifies and transmits only new or changed data blocks.
Being in hurricane territory, Vaclavik and his team were prompted by Hydril LP's board of directors to come up with a more-rapid disaster-recovery plan than Hydril's previous tape-based infrastructure allowed. After witnessing the several-day traffic gridlock ensuing from the previous season's hurricane warnings, the company was concerned it might not have such easy access to off-site tapes if a disaster ever struck the corporate headquarters.
Vaclavik decided to search for a disk-based backup/recovery solution that could encompass the backup needs of all of his company's systems, including an AS/400 with close to 1TB of production data. EVault's InfoStage turned out to be the answer.
At Hydril, InfoStage is installed in a dual-vault configuration: The primary InfoStage vault is at Hydril's main data center in Houston and is based on a Dell 1750 server with 4.5GB of usable disk space provided by a back-end EMC AX100 system. A matching Dell/EMC system located about 35 miles away acts as Hydril's InfoStage remote vault. To ensure fast recovery if both sites are impacted by a potential electrical outage, Vaclavik figures the company could even ship a few portable vault servers, equipped with the company's data, to the company's collocation facility located in the northeastern US
With the compression functionality, Vaclivik claims that backing up the 1TB of AS/400 data to the remote vault now only requires 150GB of disk space. In fact, backing up a total of 12TB of production data from Hydril's Windows and Linux servers, along with the AS/400, requires less than 2.5TB of disk space for compressed backup copies that exist on either the local vault or the remote vault.
"The compression ratio is phenomenal," says Vaclivik. "What's nice is that the system does bit-wise changes. If you have an SQL Server database and just two records in the database change, the only thing replicated to the vaults is those two records."
Michele Hope is a freelance storage writer. She can be reached at firstname.lastname@example.org.