Tandberg Data BAKStor 1000-12 review

Tandberg Data’s new BAKStor appliances show the versatility of iSCSI. They combine masses of near-line storage and present it to the network as virtual disk or tape drive targets. This makes the BAKStor unique, as it’s the first iSCSI storage appliance on the market to support both disk and tape targets in the same device.

Tandberg has been busy acquiring storage technologies as it bids to break out from its tape-drive heritage and diversify into other storage markets. The BAKStor products came about after Tandberg acquired the Manchester-based Computer Design Group Plc this year, making these new appliances largely a home-grown UK affair. The main thrust of the product family is to bridge the performance gap between traditional tape and disk-to-disk data backup by providing fast near-line storage.

The BAKStor isn’t a replacement for tape but more an intermediate backup stage that still allows data to be migrated to tape. The appliance has a separate SCSI controller card for attaching physical tape drives and libraries and using them to backup data to removable media. Another key feature is high-performance data restoration, as you don’t need to load a tape whenever a user calls for a lost file to be resurrected. Tandberg advised us that its research with a number of ISVs (independent software vendors) and ISPs showed that the majority of restore requests occur within the first three to five days after a file is backed up. The BAKStor iSCSI target currently emulates an Ultrium LTO-2 tape drive, which means it can work with any network backup software that supports this hardware. Presenting network hard disk storage as a virtual iSCSI tape drive means the servers and the backup software see them simply as locally attached devices that require nothing more than the normal Windows drivers loaded.

Tandberg claims a ten-minute installation is possible, and the BAKStor is indeed easy to install and configure. The web-browser interface is a bit rough and ready but easy enough to get on with. Your first job will be to create your software-managed RAID arrays. Next, you create storage slices, which Tandberg likens to disk partitions. You decide whether your slice is to be an iSCSI disk or virtual tape device, give it a meaningful name and enter its maximum size. All tape slices start out at 10GB in size and dynamically grow as more data is written to them. The latter parameter determines the maximum slice size, and for a virtual tape the appliance will issue an ‘end of tape’ command to the backup application when this limit has been reached.

Snapshots provide a local backup facility and you can decide what percentage of the source slice size they should use as their own storage space. Mirroring is possible if you select a snapshot size of 100 per cent. As soon as a snapshot is created it appears as an iSCSI target, so you can log on and use it to restore data back to the original slice or any other for that matter. The AiiR (Automated Internal Intelligent Replication) feature takes this a stage further by offering an automated file versioning system, which takes snapshots at scheduled intervals and retains older ones according to your rotation settings.

There isn’t much to do for iSCSI configuration, since the appliance handles all naming conventions automatically and you can use CHAP authentication for access control to specific targets. It’s important to ensure you choose a sensible naming convention for your disk and tape slices, as the BAKStor appends this to the end of the target’s IQN. When configuring an initiator this will be the only means of determining whether available targets are virtual disks or tapes before logging on to them.
For testing, we used a single Gigabit Ethernet link to the appliance and created a RAID0 stripe across two drives, which we split into virtual disk and tape slices. Using Microsoft’s Software Initiator 1.06, we logged on to a virtual tape slice whereupon our Windows Server 2003 system automatically loaded its embedded LTO-2 driver. CA’s ARCserve r11 also had no problem recognising the virtual tape drive and reported an impressive 26.4MB/sec while securing a 9GB mixture of test data from the server. Performance for standard iSCSI disk targets was reasonable, with the open-source Iometer reporting transfer rates of 76MB/sec with two workers.

Backup facilities to local tape drives or tape libraries extend to selecting a slice and scheduling jobs for regular intervals. You can request a snapshot to be taken prior to the job starting, but bear in mind you can only secure or restore a disk or tape slice in its entirety and can’t view the contents of the physical tape. We successfully ran tests using a Tandberg Data SDLT600 and saw backup performance of 15MB/sec while securing a disk slice.

Combining virtual tape and disk targets into a single device makes the BAKStor extremely versatile. Add in the snapshot and AiiR features, plus support for external tape drives and libraries, and you have a storage system that brings out the best in iSCSI.