Birth of a Tape Library Behemoth

EMC's DLm 8000 is its brawniest ever mainframe (virtual) tape library.

There's just something about the month of August that brings out the fight in storage giant EMC Corp. In August 2011, for example, it introduced a revamped version of its Disk Library for Mainframe (DLm), the first version of the product to incorporate the best-of-breed virtual tape library (VTL) technology EMC inherited via its late-2010 acquisition of Bus-Tech Inc.

This August, EMC kicked off its latest attempt to lay siege to the mainframe (tape) world: the DLm 8000, a renamed, Big Iron-ready version of its high-end VMAX scalable storage arrays.

EMC says its biggest and brawniest DLm system supports its Symmetrix Remote Data Facility (SRDF); a key selling point is its ability to maintain consistency in backup or business continuity planning (BCP) scenarios. Although SRDF is chiefly deployed to support replication across SAN or IP networks, EMC, pitches it as a means to support synchronization and replication between geographically distributed BCP sites.

EMC is by no means a new player in the mainframe tape space. That said, it arguably went on the offensive in November of 2010, when it acquired Bus-Tech, a vendor that had been EMC's partner for the better part of six years. (EMC's acquisition of Bus-Tech occurred in Q4 2010, during which time mainframe sales broke several records.)

The DLm 6000 system EMC delivered last year boasted backup speeds of up to 2 GB/s. The new DLm 8000 boasts speeds up to 2.7 GB/s of backup bandwidth.

The former system shipped with 12 FICON channels; the bigger, brawnier DLm 8000 ships with 16. That much bandwidth is almost staggering, notes veteran Big Iron-watcher Alan Radding, who writes about mainframes and enterprise computing on his Dancing Dinosaur blog.

"The DLm8000 is packed with eight Bus-Tech engines ... and it assigns two FICON connections to each engine for a total of 16 FICON ports cranking up the throughput," Radding writes in a richly informative blog post. "No surprise they can aggregate that level of throughput."

The DLm 8000 is bigger and brawnier in other respects, too. It delivers additional VTL capacity -- 2,048 VTLs compared to the DLm 6000's 1,500. The DLm 8000 also supports up to 5.7 PB of logical storage, as is true of the DLm 6000.

Why all that brawn? On the one hand, says Radding, the new DLm 8000 addresses an arcane, but likely very lucrative, technology problem.

"Synchronous replication addresses the potential problem latency mismatch that occurs with the usual asynchronous replication, where a lag between writes to the primary and to the backup target storage can result in inconsistent data.," he explains, adding that this "mismatch" typically "exists for a brief period."

For some customers (such as large banks and financial firms), the brevity of this period isn't brief enough, EMC claims. "Large financial organizations with high transaction volume ... have historically faced recovery challenges because their mainframe tape and DASD data at production and secondary sites were never fully in synch," explains Radding, citing EMC's claims.

"[R]ecovery procedures often slowed until the differences between the two data sets were resolved, which slowed the resulting failover. This indeed may be a real issue but for only a small number of companies, specifically those that need an RTO and RPO of just about zero."

Although its pitch with the DLm 8000 might be relatively specialized, the performance of EMC's new super library could notionally appeal to a larger base of mainframe customers. Its as-yet-unannounced price, however, will likely be a deal-breaker for many would-be buyers, Radding notes. "The device ... is [at] the top of its VTL lineup and VMAX enterprise storage tops its storage line. With high throughput and synchronous replication, this product isn't going to be cheap. However, if you need near zero RPO and RTO then you have only a few choices."

Among the obvious candidates, notes Radding, are IBM's TS7700-series solutions, both of which support VTL connectivity. "The TS7700 avoids the latency mismatch issue by using a buffer to get the most optimal write performance and then periodically synch primary and target data," he argues.

Another choice is Oracle Corp.'s Virtual Storage Manager and Virtual Library Extension, which it inherited via its acquisition of the former Sun Microsystems Inc. (Sun purchased tape library specialist StorageTek Inc. back in 2005.).

"The Oracle approach promises to improve tape drive operating efficiencies and lower TCO by optimizing tape drive and library resources through a disk-based virtual tape architecture," suggests, Radding, who notes that Hitachi Data Systems also markets a mainframe tape backup/VTL offering.

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