To improve backup speeds and restores, virtual tape library (VTL) users are keeping more and more backup data online rather than spooling it off to tape, but the costs are mounting.
Instead of a few days of backups, users routinely hold weeks, if not months, of backups on their VTLs, according to Don Mead, vice president of marketing at storage software vendor FalconStor Software Inc. One customer has more than a petabyte of backup data stored on a VTL, he said. "When we first introduced [our] VTL, we never imagined the amount of data users would put behind it."
One way a VTL can soften the financial blow of storing backups online is by compressing the data. Some VTLs, like FalconStor's, do software-based compression and Neartek Inc. recently announced that its Virtual Storage Engine 3.0 is equipped with a PCI (Peripheral Component Interconnect)-based GZIP hardware compression board for up to 2:1 compression without degrading performance.
Longer term, however, VTLs will probably adopt a more aggressive compression technique -- data reduction. Data reduction keeps track of the blocks the VTL has seen and, rather than storing a block it has seen previously, it only stores a pointer to it. In the data protection space, Data Domain and Avamar Technologies Inc. both use data reduction in their data protection platforms. Last summer, EMC Corp. VTL spin-off Diligent Technologies Corp. announced its ProtectTier platform with data deduplication technology that can reportedly provide up to 25 times data reduction.
Data Domain has also announced that it will join the VTL fray and add a VTL/Fibre Channel interface to its platform rather than the Ethernet-accessible file system interface it has used this far. "There are some cases where Fibre Channel is the default [in the data center] or where a tape library is the only thing that they understand," the firm's Biles said. "VTL is just an interface," he noted, so by adding a VTL interface, "we're just saying it's a nonissue."
Mead said FalconStor will also introduce data reduction technology this year. That's significant because FalconStor's VTL software is at the core of numerous VTL offerings, including 3Par Data Inc.'s new utility VTL, Copan Systems' Revolution family, EMC's Clariion disk library and Sun Microsystems Inc.'s VTL. It's also thought to be behind IBM's Virtualization Engine TS7510.
But Data Mobility Group's senior analyst Dianne McAdam warns users not to let their expectations for data reduction get too high -- at least not at first. One user McAdam knows reports getting 17:1 compression but it took him six weeks to see it. "You don't get it right off the bat, McAdam said, adding that the data reduction software has to start "seeing the repetitive patterns."