There has been a lot of talk about hybrid storage arrays. That term, to most people, means some kind of arrangement of hard disk drives (HDD) and flash. But suddenly, the market has seen a flood of products that team up tape with disk and/or flash.
David Cerf, executive vice president of strategy and business development at Crossroads, is an advocate of a hybrid disk and tape system. To work and gain acceptance, he said, such an approach has to fit how users are currently operating and shouldn’t ask them to change their behavior. In addition, he said that data protection should be ingrained.
Dternity, he said, meets these criteria. It is a gateway architecture that lets users look at files or objects, as well as being able to access tape, disk, flash, disaster recovery (DR) or the cloud.
“Dternity is the first Linear Tape File System (LTFS) solution for disk and tape,” said Cerf. “It is a Network Attached Storage (NAS) appliance designed for unstructured data.”
The solution provides shared storage for online, nearline and archiving. Cerf added that everything lands in the disk-based appliance as it is faster to write it there. It then feeds everything to tape. Automated policy determines what data goes where and when. For DR, second and third copies can be created to be stored in different places.
Cerf also announced the availability of Dternity as a VM for free download instead of being delivered as an appliance, as well as the Dternity Media Cloud which is an off-premise storage service. This gives the user a second copy of data as a service.
“We can take old tapes in any media and convert into something stored offsite,” said Cerf. “The media belongs to you.”
The concept of combining tape and NAS appears to be gaining traction. HP calls it tNAS. This solution permits users and applications to access data on tape-based storage via disk cache without the need to manage media cartridges. Similar to the Dternity example, data is staged to a disk cache and then written to tape as tape drive resources become available.
“The bottleneck is typically the disk cache as it has to cope with data in, data out, file stubbing and updates to the archive volume database,” said Chris Powers, vice president of the data center development unit at HP. “A well configured disk cache will allow a maximum throughput of 140 MB/sec per archive volume. An LTO-6 tape drive supports 160 MB/s native, so it can keep up.”
Alternately, an SSD-based cache can speed this up to 270 MB/s for tape. In this case, the tape drive could become the bottleneck depending on the compression rate. At 2:1 compression, an LTO-6 tape drive will support 320 MB/s. Data is written to the cache immediately and can be read at once. Data not in the cache, though, would take around four minutes to be returned as it has to be read off tape first.
Powers said such architectures were far from theoretical. He said one European research hospital was using tNAS for archiving of x-ray files. And a federal court system was using flash and tape to store video of court proceedings. In that case, the set up included an all-flash array in front of the tape.
Per HP’s numbers, the price per GB of tNAS works out at 51 cents for 190 TB, and 25 cents for 1100 TB. When SSD is added, the price drops to 45 cents for 190 TB and to 25 cents for 1100 TB. Disk, on the other hand, is 40 cents per GB for 190 TB and 37 cents for 1100 TB. Based on these numbers, the viability of tNAS increases as capacity rises.
On the performance side, disk performance is better at lower capacities. At 190 TB, disk performance is 600 GB/second while tNAS has 240 GB/s and tNAS with SSD is 320 GB/s. But once you hit 1100 TB, the 1080 GB/s of tNAS and tNAS with SSD beat the 1000 GB/s of disk.
“Substituting SSD for HDD in the caching layer shows big dollar-per-GB benefit as throughput performance allows for infrastructure cost avoidance,” said Powers. “For this architecture, however, larger file sizes are better as anything smaller than 4 MB will impact performance.”
He said that organizations should be asking, "Can you wait four minutes on data?" If not, what is the maximum age of the data that actually needs this faster access time? With a real answer to those questions, organizations can determine how to configure their archiving needs.
DDN has been a high-performance disk vendor for many years, but as a sign of the times, it is now adding tape to its repertoire. Such an occurrence probably hasn’t taken place for at least a decade – the trend has always been for mainline disk vendors to denounce tape. DDN’s design will add tape as part of an active archive.
“Tape not a separate system, it’s just another pool of your storage,” said Molly Rector, chief marketing officer at DDN. “This requires seamless management between media.”
In this solution, flash is used for high IOPS and tape for high throughput, which Rector said is a vital combination for big data.
Spectra Logic has just released a Shingled Magnetic Recording (SMR) disk product called ArcticBlue which leverages a hybrid storage architecture and SMR media to create an object storage-based disk platform that is said to deliver longevity, efficiency and cost effectiveness along with the performance of online disk.
“ArcticBlue creates an on-premise cloud with an S3 interface to make deep storage more accessible,” said Spectra Logic CEO Nathan Thompson.
He added that it has built-in compression and brings storage costs as low as 9 cents per GB for 2 PB of network attached storage.
“It gives bulk storage for archiving, backup and unstructured data, but is not for databases,” said Thompson.
Tom Wultich, senior director, Oracle archive product & program management, gave some perspective of how far storage density has come. “Back in 1998, the storage of 10 PB required eight acres and now can be accomplished within 37 square feet on tape,” he said.
He suggested that disk could be incorporated into tape solutions as a home for metadata. This would make it fast to find where in the archive the right file resided. It could then be retrieved more quickly from tape. Oracle has done some work on tape and NAS combos with QStar and more announcements should be expected on this line going forward.
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