Copan Systems' Revolution 200T is potentially a really revolutionary system. It is the first backup library built using disk drives instead of tapes. Because it offers restore and backup at disk speeds rather than tape and is scalable to 224TB of capacity the device can function as a disk-based backup store. With most of the drives powered down and RAID used to protect against drive failure, the device has the security and cost profile of a tape library. Here we provide a closer look at the system

Configuration
It occupies a standard 19 inch rack and can have eight shelves of disk, up to 896 disks in all. Each shelf holds separate canisters of disks. A canister is similar to a tape library's magazine. There can be eight canisters per shelf and each canister can hold fourteeen drives. They are mounted vertically in two rows of seven. Currently Hitachi 7200rpm 250GB SATA drives are used.

Camberley Bates, Copan's VP of marketing and business development, says, "The canister has the ability to be removed and is for servicing. However at this time we have not announced the portability option."

Only a quarter of the drives are spinning at any one time. There is an 'overdrive' function which lets 27 percent of the drives spin. This limitation is to keep down the power budget, lower heat, reduce cooling needs and avoid vibration; all factors which allow the drives to be packed closely together. (This is the MAID idea.)

The minimum configuration has 56TB of capacity; that is two populated shelves. Upgrades are in 28TB increments.

The system is managed via the GUI-based Revolution Management Console, which can be accessed locally on the unit or remotely.

Reliability
There are four disks per shelf set aside as spares and usable by any canister in the shelf. That means 1TB per shelf is not available to store data.

If operational disks fail then a spare is bought into service, with a RAID reconstruction process. There is no pause while a failed disk is located and replaced. RAID 5 is offered together with RAIV - redundant attay of independent volumes.

A disk monitoring system called Disk Aerobics checks the status of the disks. It uses SMART data from the drives for drive status monitoring. For each drive the time spent powered on is tracked, together with its idle time, its starts and stops and temperature.

Bates says, "Disk Aerobics will kick in before a drive fails, if it detects a level of errors, and revitalize the data by moving it to a spare. This avoids RAID rebuild. If the drive fails, the system then goes into RAID rebuild (power budget in the background is used to minimize impact to performance). Normal service is used to replace dead drives."

Alerts are sent out using SNMP. The power supplies have N+1 redundancy and are hot-swappable. There are multiple and redundant cooling fans.

I/O
Connection to host servers is by 2Gbit/s Fibre Channel. There are two such ports on an entry-level system and four on the 224TB configuration. The transfer rate is 240MB/sec for reads and 180MB/sec for writes with the entry-level configuration. With the maximum configuration the figure is 720MB/sec for both reads and writes. Copan quotes a figure of 2.4TB/hour for this system.

Tape emulation
The starting system can emulate from two to fourteen tape libraries, which are virtual tape libraries. This can grow to a total of 56 emulated libraries with the high-end system. Each emulated library can have 56 virtual tape drives.

The list of emulated tape libraries is:-

- ADIC Scalar 100, Scalar 1000
- Quantum P1000, P3000, P4000, P7000
- HP ESL9000
- StorageTek L20, L40, L80, L180, L700, 9710, 9714, 9730

Emulated formats are:-

- IBM/HP LTO-1, LTO-2
- Quantum DLT 7000, DLT 8000, Super DLT1
- StorageTek 9840, T9840B, T9940A

Compression is used on backed up data. No figures are available for compressed data capacity. We might assume that a 1:2 compression ratio is available. It could be more; it could be less.

There is no emulation of IBM or Sony formats. The only suported backup software products are Veritas' NetBackup, Commvault's Galaxy and Bakbone's NetVault. These have to be running on Solaris or Linux systems.

The lack of general backup software support and the restriction to Solaris/Linux hosts suggests that the interface to the Revolution 200T has to be produced specifically for each backup product.

Copan provides comparison data for the Revolution 200T and a StorageTek L700 library. It says that maximum usable capacity for the Revolution 200T is 162-182TB but 125TB for the L700. The StorageTek unit can have 40 tape drives, the 200T ofers 56 virtual tape drives (and up to 2,048 'catridges' of user-defined sizes). 200T throughput is 720MB/sec with the L700 offering 35MB/sec. Two percent of the cartridges in the L700 can have simultaneous access; it's 25 percent for the 200T. The L700 offers 8.49TB/sq ft of floorspace; the 200T offers 24.3.

Copan says its system is easier to manage in that migration of data from cartridge to catridge is not needed in a disk-based system.

Controller
The virtual tape libraries and tape emulation are provided by the controller. It takes the raw rack of disks and gives it a personality. The prospect is that other personality types could be offered in the future. One that springs to mind is a fixed content store, perhaps using content addressing.

The rack controller is an X86 CPU which provides the virtual library functionality. It can have either two or four Fibre Channel ports. It links to shelf controllers which have a cache and are dualled for failover. These implement the RAID protection scheme. They convert the Fibre Channel signals to Serial ATA and talk to individual canister controllers.

Scalability
Revolution 200Ts cannot be bolted together like a tape library having additional modules added with the robotics extended. But customers could have more than one Revolution. Bates says, "We do not claim to scale larger than tape libraries in a single cabinet. We are denser than the other libraries, so (need) less floor space: i.e. 22TB versus 13TB for a Scalar 2000."

"In terms of scaling, yes the Powderhorn scales larger as does the (ADIC) 10,000. For libraries like (the) L700 or the Scalar, just like you can manage multiple libraries, you can manage multiple Revolution 200T's."

A tape library vendor view
Overland Storage provides tape libraries. It has also introduced disk-to-disk-to-tape (D2D2T) products and so is conversant with using disks as a backup target. Henrik Hansen, marketing director for Overland Storage, thinks, "Tape technology and more importantly tape automated libraries will not be replaced by pure disk-based systems in the short to medium term."

"As long as tape remains a more cost effective technology platform for backup and more importantly archiving it will remain the most popular technology platform for medium-to-longterm data storage." Of course it also, in off-site form, protects against natural and man-made disasters. Data off site is just more secure.

On the capacity front Hansen points out, "When our customers invest in a 100TB tape library solution it is not just limited to service 100TB of data. In most 500 slot libraries you might find 500 media cartridges installed, however in most instances the company will have 2, 3 or more times that amount of media cartridges meaning that the capacity of the library effectively is much higher than 100TB."

The Revolution 200T could be a landmark device. If other companies take the MAID route, which promises greatly lowered cost and improved floorspace efficiency, then the product could do very well. If Copan introduces a fixed content version with the same cost and floorspace advantages then it could do very well again.