RAID 3 re-appears
An old RAID level re-emerges
By Chris Mellor | Published: 11:00, 16 September 2004
It's amazing how supposedly commodity technology can keep on getting re-invented and improved by small and nimble companies. NetCell is a case in point. It is a privately-help company that says it has solved a well-known RAID 5 problem with technology called SyncRAID.
Apparently its SyncRAID RAID 3 products offer RAID 0 (mirroring) performance with RAID 5 (parity and striping) protection.
THe company states: "Like traditional RAID5 products used in mission-critical enterprise applications, NetCell's SyncRAID technology uses a striped-parity approach that stores redundant backup information in case any individual drive fails and the data must be regenerated. However, instead of employing RAID5's read-modify-write process, which degrades write performance, SyncRAID implements an on-the-fly XOR approach so that parity calculations can occur at the maximum rate of the disk drive's input/output (I/O) for both reads and writes, in parallel. As a result, the existence of the dedicated protection drive does not reduce the additive performance of the main drives, and users can achieve the fastest disk array possible using low-cost, off-the-shelf drives. This is extremely important as disk I/O speeds increase beyond those of current serial ATA products."
If your application is a streaming video one then a multi-second pause while the RAID controller works out that one of the RAID 5 disks is broken isn't desirable. Neither is any resulting slowdown in performance while the broken drive is being lived with until it's repaired.
NetCell has recently unveiled two storage processors using SyncRAID acceleration technology. In addition to the performance benefits there is a one-button automatic configuration of all drives in the array at start-up. The NC3000 is a 3-port device and the NC5000 has five ports. Both attach to a PCI or PCI-X bus and support ATA and S-ATA drives. Installation is driverless.
Both the NC5000 and NC3000 processors employ both a RISC engine and hardware accelerators. The hardware on-the-fly XOR and switch engine ensures that parity protection data is created with zero loading. An on-board MIPS RISC CPU supports data cache algorithm management, along with the standard RAID level functions and drive monitoring functions.
The processors are priced to enable the development of mainstream PC storage adapter cards that provide RAID 0-Class performance and RAID 5-Class data protection with an MSRP starting at $179.99 for 3-port cards and $249.99 for 5-port cards.
In its RAID 3 set-up one of the drives is set aside to store parity information. Data is striped onto the other disks in the array.
Parity protection is implemented using the wire speed XOR engine, which eliminates a read-modify-write sequence found with traditional striped-parity RAID engines. Netcell claims this effectively doubles performance compared to RAID 5 cards in similar applications.
In a 5-drive 7200 rpm ATA drive configuration, NetCell says the NC5000 delivers an effective 190-200 MB/sec of sustained read throughput, and up to 110-120 MB/sec of sustained write throughput, for a parity-protected array with up to one terabyte of storage capacity using standard 250 GB drives that appear to the host as a single large disk. This is apparently soon to be two terabytes with next-generation drives.
NetCell's NC3000 and NC5000 processors can also be used in External Serial ATA implementation in support of the recently adopted SATA International Organization (SATA-IO) standard.
Because of its pricing and the use of S-ATA drives, NetCell makes a strong claim for price-effectiveness: "It will be possible to create (a) one terabyte 'super drive' at as little as one-seventh the cost of an equivalent enterprise-class SCSI-based RAID5 storage unit, while achieving up to twice the write performance for large streaming files."
Get a NetCell SyncRAID white paper here.