With a new PathLight VX450 disk-to-disk (D2D) backup product to punt, ADIC's Steve Mackey is doing the rounds of customers and the media. Techworld asked him about this, Microsoft's DPM and HP's new virtual tape library.

Regarding DPM, Mackey reckons both products, DPM and PathLight VX450, are aimed at mid-tier enterprises. Microsoft says DPM is for the 5-49 server shop and Mackey says, "VX450 is for the 2-5TB of data" shop.

Mackey believess the key thing is process change or, rather, its absence. ADIC's VX450, with all the software functionality of its big brother, the VX650, but in a cost-reduced package, can be slotted right in to an existing backup to tape setup using ADIC libraries. Mackey say it means, "No process change. Existing backup software and processes can be used" without interruption. Not so with DPM.

Another thing is that there is just one backup process; not one to disk and then a second and different one to tape.

PathLight embeds the tape function such that it 'bleeds' data off to tape once a VX retention policy condition is met, such as a 30 day period. There is no need to run a separate Veritas or Legato backup session to accomplish this.

Equally restoration processes are essentially unchanged whether the file to be restored is on the VX' disks or has been archived off to a tape library. The same backup software interface is used to do this.

Not so with DPM. Microsoft's product, according to Mackey, requires that users alter their current backup process, if they have one of course. They have to buy a DPM server and set up agents on the target servers and then set up the process to have server files backed up to the DPM server; full initially and then the incremental changes.

Then they have to get a new version of their backup software product, one modified to support the DPM server as a target device and backup its data to the tape domain. The restore process is different too. Mackey points out that users have one restore process for recovering files from the DPM server, using a Microsoft user interface, and a second process, using their backup software's interface, to recover files from the tape archive.

Mackey says: "This surely adds complexity as well as process change to the situation. Our research shows that a vital issue is not having process change. In a mid-range data centre they have very few staff. That's a massive increase in complexity." Process change is especially disruptive here.

Furthermore, it's obvious that the backup to tape from the DPM server is not automated, leading to many of the problems that Microsoft identifies as making D2D backup necessary in the first place: error-prone manual procedures; complex restores; etc.

Mackey says these problems don't exist with PathLight, with its embedded path to tape and unfication of disk and tape backup into a singfle integrated function.

Diferent problems exist for HP's VTL, "Based on Sepaton' according to Mackey: "Most D2D products seem to have been designed with tape as an afterthought, or with the aim of getting rid of tape; Sepaton means 'no tapes' read backwards. Data goes onto disk and it goes no further unless you back it up again, meaning a second session."

Both products; DPM and PathLight VX450, are aimed at mid-tier enterprises. Microsoft says DPM is for the 5-49 server shop and Mackey says, "VX450 is for the 2-5TB of data" shop.

Restore time
What about DPM's restore time advantage? It isn't an advantage according to MacKey. From disk both DPM and PathLight are in the same restore speed area. From tape PathLight should be fast enough not for it to matter. MacKey says the same interface is used which reduces complexity and should help increase overall restore speed a little. He recons it takes about a minute to load and get a file streaming off a PathLight's back-end tape library, once the on-disk catalogue has been used to identify the file. The end-to-end filec restore from disk time could be 30 seconds. If it's 60 seconds from PathLight's backend tape library then that, MacKey thinks, is neither here nor there.

Sizing the backup disk amount
MacKey says ADIC has a thorough and comprehensive PathLight VX disk sizing tool that takes into account the ammount of data to be backed up, its possibly varying recovery time objectives, and its likely growth. Ths data is used to provide a precisely-sized PathLight VX with no excess disk space. He doesn't know whether Microsoft has an equivalent tool. If it doesn't then sizing the DPM server's disks could be a pretty hit-and-miss affair.