By Heidi Biggar
With the release of its TotalStorage Enterprise Tape Drive 3592 last month, IBM has made it possible for its customers to use a single tape technology for both capacity- and access-intensive applications.
The 3592, which succeeds the 3590, has a 300GB native capacity and 40MBps native throughput. This compares to 60GB and 14MBps, respectively, for the 3590, and 200GB and 30MBps for StorageTek's T9940B, which was introduced a year ago.
"IBM has jumped ahead of the competition with the 3592," says Dianne McAdam, a senior analyst with the Data Mobility Group consulting firm. "The drive has higher performance and greater capacity than previous enterprise tape drives—and it is priced reasonably."
IBM points to the increase in the number and types of regulations—in particular, new healthcare, automotive, and financial regulations—as key factors driving user demand for higher-capacity and faster-access tape drives.
"Users are caught in a dichotomy," says Bruce Master, senior program manager of worldwide tape product marketing at IBM. "They're being pressured to do more with less, while being asked to manage more data for longer periods of time—and to provide fast access to that data."
While disk is an attractive alternative to tape in some backup environments, IBM expects tape to continue to play a key role in primary backup for a variety of reasons, most notably lower cost and media removability.
IBM will initially offer the 3592 with a 300GB cartridge; a family of cartridge capacities and types (e.g., write once, read many, or WORM) is planned. In the meantime, 3592 users can format the 300GB cartridges as 60GB cartridges when fast access, not high capacity, is needed.
The average access time to retrieve one byte of data from a 60GB-formatted cartridge is 33 seconds, compared to 61 seconds from a 300GB cartridge. Media for the drive is available from Fujifilm.
To boost throughput from 14MBps to 40MBps, IBM increased the size of the buffer used in 3590 drives from 16MB to 128MB. "The larger buffer size allows the tape to keep moving as much as possible, which reduces the occurrence of back-hitching," explains McAdam.
Unlike disk systems, most tape drives cannot adjust to variable host speeds, so if a host is slow the tape drive is forced to stop and wait for the data stream to "catch up." This stop-and-start action can stress the media (the tape moves back and forth below the heads in a shoe-shine fashion) and significantly affect performance.
"Tape drives run most efficiently when they receive and write data in a continuous data stream," explains McAdam. "When data is received and written in bursts, the drive is forced to stop between bursts and reposition itself [i.e., back-hitch] for the next burst of data. Back-hitching is expensive not only in terms of performance but also in tape wear."
The 3592 avoids this issue by writing data to the tape buffer, not to the tape, says McAdam. Once a block of data is written to the buffer, the application sends a "sync" command and the data is written to a temporary spot on the tape while the drive keeps moving. As new data is fed to the drive's buffer, data in the temporary areas is copied to a permanent location.
The 3592 is available with support for AIX, Windows, and Linux, with broader platform support expected later this month. The drive can be integrated into the IBM Enterprise Tape Library 3494, for up to five petabytes of capacity, or StorageTek's Powderhorn libraries, or can be used as a stand-alone device. It is priced at $32,000.