EMC has announced a disk-to-disk (D2D) backup system in the form of two disk libraries. It will ship a low-end DL300 and a high end DL700. Unlike a tape library where a robot arm transfers tape cartridges from storage slots to and from the drives, a disk library's drives are available all the time.

Techworld has previously described this idea. Since each disk has its own drive there is no need to move them, unless off-site storage is needed. The software needed to drive a "disk library" is backup software plus extra to administer the library if the drives stay in the cabinet permanently. Additional library management software is needed if the drives are removable and can be stored elsewhere - for example, bar-coding to verify their identity.

A D2D device may also need virtual tape software so that standard server backup software products, such as Veritas' NetBackup or Legato's Networker, can operate unchanged and act as if they are backing up to a tape drive.

Legato's 7.1 version already has a disk backup option - Legato NetWorker DiskBackup Option (DBO), so high-capacity, high-speed disk arrays such as the EMC Clariion can be used to recover data faster, protect data faster, and increase performance.

EMC's new disk libraries emulate existing libraries: ADIC Scalar Series (DLT, SuperDLT); ATL P-Series (LTO, LTO-2); and StorageTek L-Series and 97xx Series (9840, 9940 formats). EMC's CX300 and CX700 Clariion serial ATA (SATA) arrays have up to 13TB and 60 drives (CX300) or 58.4TB and a maximum of 240 drives (CX700). The DL300 and DL700 disk libraries are based on these RAID-protected arrays. With a claimed 3:1 compression ration capacities rise threefold.

A 1TB raw capacity DL700 would cost around $450,000, possibly £300,000 in the UK. This is almost half as much again as a comparable tape library. The cost increase is justified by EMC on performance grounds. Backup speeds are said to be 30 to 60 percent faster, compared to LTO1 (60 percent) and LTO2 and StorageTek 9840B (30 percent).

Restore speeds are almost twice as fast, because tape libraries have to transfer a tape to a drive and then find the file to be backed up. The normal time taken to backup to tape, the so-called backup window, is being dramatically shortened. There is mention of automatic movement of files from the disk library to tape. However, this will require customers to purchase, or use, an existing tape libray, from the ones mentioned above.

StorageTek's director of operational strategy, Tod Rief, said that a mid-market version of the recently-introduced StreamLine SL8500 library will be introduced containing an integral SATA disk cache, tape virtualisation software and support of multiple half inch tape formats. This would be a simpler purchase in that it will be an integrated solution, he said.

For EMC this is another plank in its information lifecycle management (ILM) offering. However, EMC may still feel that it needs an EMC-branded tape platform to fill out its ILM storage tiers.

It seems likely that D2D backup is going to become a standard offering. Get prepared to receive a deluge of backup window abolition messages from your vendor.