Of all the mid-range backup tape formats currently available, SDLT (SuperDLT) has evolved the fastest. When SDLT220 was launched at the beginning of 2001 it was the first format to break the 100GB native storage barrier and uniquely, the second generation SDLT320 was delivered in less than a year and was the first to top 1GB/min backup speeds.
No other format has metamorphised at that sort of speed. And now we have the SDLT600 to review, making this the only mid-range format that's in its third generation. Not only that but it takes native backup speeds above 2GB/min and also delivers a whopping 300GB of native storage – the same as IBM’s TotalStorage Enterprise Tape Drive 3592 which the company claimed as the world’s highest capacity enterprise tape storage device until Sony’s SAIT
dropped in at the end of 2003.
SDLT introduced a number of new features and first up is Quantum’s laser-guided magnetic recording (LGMR) technology. The servo tracks used to ensure media are precisely positioned in relation to the read-write heads have traditionally been placed on the same side of the tape used to record data. Essentially this is a waste of space as more tracks means higher capacity so, to free up more surface area, Quantum opted to laser etch the servo tracks on the back of the tape. A pivoting optical servo (POS) system is used to carry out tracking and this incorporates an improved PRML channel and magneto resistive cluster heads. Storage capacity over SDLT320 has been increased simply by upping track density from 1,058 to 1,490 tracks per inch.
The SDLT600 is backward read compatible with DLT media but to achieve this an extra read head had to be built in as the LGMR head only works with SuperDLTtape media.
Overall, compatibility is disappointing as it can only read SuperDLTtape 1 tapes so you can’t re-cycle your current media after upgrading your drives. However, it can also read DLTtape VS1 media so you can migrate from Quantum’s budget-based ValueSmart tape drives.
As the SDLT600 is capable of such a high performance we opted to bring the latest iSCSI products in the test environment to allow the drive to stream freely. An Overland Storage REO Series RA2000 backup accelerator was linked over Gigabit Ethernet to an Xinit Systems Sharqserv 124-G2 rack server equipped with dual 2.4GHz Xeon processors.
The server was installed with Windows Server 2003 and the drive connected to a dedicated Adaptec Ultra320 SCSI host adapter. We used Microsoft’s iSCSI initiator software to establish a session with the RA2000 and configured four of the REO’s Serial ATA drives as a RAID-0 striped array. A quick test with the open-source Iometer returned an average transfer rate of 65MB/sec which was more than enough bandwidth for the SDLT600.
Whilst securing an 8.5GB mixture of test data the SDLT600 returned close to its quoted native transfer rates with Computer Associates ARCserve 9 and Veritas Backup Exec 9.1 for Windows Servers recording average speeds of 2,085MB/min and 2,007MB/min. Restore rates were equally impressive with the test data returned to its original location on the REO at 1,637MB/min and 1,503MB/min respectively.
Quantum’s new DLTSage xTalk Windows utility delivers sophisticated drive diagnostics and it supports any DLT, SDLT, LTO or VS drive. Full diagnostics tests including health checks on the drive and error checks on media can be run and Quantum now requires that all faulty SDLT drives are screened with this software before being returned.
If you haven’t already made a selection then your options for mid-range backup are simple enough – Ultrium or SDLT. However, while our tests verify that SDLT is the fastest currently available it’s worth noting that Ultrium 2 is only a whisker behind this in terms of performance and the third generation should be due out in the next twelve months. Of the two formats Ultrium is the wiser choice and clearly already a favourite as a report by Gartner Dataquest
has revealed Ultrium was outselling SDLT by almost two to one.
The choice is simple. If you’re looking to a new mid-range backup format to migrate to then go for Ultrium as it is only on its second generation and offers a better future but those who plumped for SDLT won’t be disappointed with this third generation