Hewlett Packard’s AutoRAID technology greatly improved the stability and security of early RAID systems – without sacrificing performance, and is the model around which most RAID setups are designed around today. By allowing users to add and replace disks anywhere in the array, it granted the flexibility that previous RAID iterations could not. It was a key step in the mass adoption of RAID technologies throughout the small business arena.
Those who have seen the product feel it is a noteworthy improvement over existing RAID systems. “It’s a very significant announcement for the entire industry,” said Tom Lahive, senior analyst at International Data Corp. (IDC; Framingham, Mass.). “The beauty of it is that most other vendors are just starting to integrate some type of software management. What HP has done is make a controller that has more intelligent features than most others. It really, truly is automatic RAID.”
A key technique of AutoRAID is dynamic data migration, which enables the system to use different RAID levels to provide quicker data accessing or lower-cost storage. Data being actively used is moved to RAID 0 or 1 level, in much the same way that common disk drives move active data to cache memory. Constantly moving data within the array balances overall performance and cost, HP said.
“With current systems, you have to select two of the three parameters people want with RAID: low cost, high performance and high availability,” said Roger Buckthal, project manager at HP’s Storage Systems Division. “The underlying innovation is a new way of addressing. Our mapping technique maps the host address to the disk address in a dynamic way. The dynamic algorithm is the key for us to change the active data to levels 0 or 1 to provide performance and put less active data in level 5, which is more cost effective.”
Buckthal noted that although HP is providing details about the different RAID levels, users no longer have to master the fine points of which level is best for different requirements because AutoRAID constantly moves data around automatically.
“We’re trying to get away from talking about the levels,” said Joe Molina, chairman of the RAID Advisory Board (St. Peter, Minn.), a trade association. “Users spend a lot of time worrying about those levels when they should really be thinking about performance, price and reliability.”
The HP system also permits on-line expansion. When drives are added, the management software reconfigures the system to take advantage of the additional capacity. Both active data and parity data used for on the new drive. This technique can also be used to replace failed drives.
“Another thing that’s different about this system is that when you add drives, disk capacity is not important,” Buckthal said. “We treat the disks not as complete disk drives but as blocks of storage. All the drives together are like a large pool of storage.”
He noted that this technique also makes it possible to use some of the capacity of a so-called hot spare for active data. Traditionally, a hot spare is kept powered up, holding mainly parity data. When a drive fails, the hot spare is called into play.
The HP technique uses some of the capacity of the drive, but distributes most of the spare capacity across all the disk drives in the array. That capacity is kept empty, so that space will be available when a drive fails. Spreading the data around helps improve performance, Buckthal said.
Treating disks as blocks of data also eliminates the tricky problem of spindle synching, which has been necessary to make sure that data comes off the individual disks at the same time. It also lets HP intermix drives that have different spin rates, which makes it simpler to upgrade systems as technology advances or budgets are fattened. Drives provide identification information so the controller knows what capacity and performance traits each drive has.
If there is one issue with the AutoRAID format, it’s that the drives do have the tendency to fail.
“The AutoRAID setup is very progressive, and does have some protections against RAID array failure,” says Len Travers, data recovery technician with Irvine, CA’s Hard Drive Recovery Associates. “Recovering these arrays, on the other hand, can be a major chore. The disk setup is far less recoverable than your regular RAID 5 machine.”
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