PowerEdge Cost Effective RAID Controller. Designed for a great price/performance balance, the CERC ATA100/4CH incorporates many of the features once limited to SCSI controllers, such as a powerful on-board processor, CACHE memory, and support for RAID-5. This controller supports RAID levels 0, 1, 5, and 10.

PowerEdge RAID Controller, Dual Channel. The PERC3/DC is a dual channel 64-bit, 66 MHz PCI RAID card. With 128MB RAM for cache and an integrated backup battery, it can be unplugged and moved to another machine while preserving all buffered information up to 72 hours after a server power failure. Fully hot plug compliant, it supports RAID level 0, 1, 5, 10, and 50. It supports the same combination of internal/external channels as the PERC3/DCL.

PowerEdge RAID Controller, Dual Channel Light. The PERC3/DCL is a "light" version of the PERC3/DC card, having less RAM and no cache backup battery. It is a dual channel 64-bit, 66 MHz card with 64MB RAM cache that supports RAID levels 0, 1, 5, 10, and 50. It is a PCI card that is fully hot plug compliant, and can handle two internal, two external, or one internal and one external connection simultaneously.

PowerEdge RAID Controller, Dual Channel, integrated. A ROMB solution, the PERC3/Di is built into the PowerEdge 4600. It is capable of handling RAID levels 0, 1, 5, and 10. Like all PERC3 controllers, it uses the i960 100MHz processor and can operate either one internal or one internal and one external channel concurrently.

PowerEdge RAID Controller, Quad Channel. The PERC3/QC is a four channel 64-bit, 66 MHz PCI RAID card. It has a single 128MB RAM cache DIMM, includes the same backup battery functionality as the PERC3/DC card, and supports RAID levels 0, 1, 5, 10, and 50. It supports up to two internal channels with the balance (up to four total) running external RAID connections.

PowerEdge RAID Controller, Single Channel. The PERC3/SC is a single channel, 32-bit, 33 MHz card with 32MB RAM cache that supports RAID levels 0, 1, 5, 10, and 50. It is a PCI card qualified with one internal connection to support PowerEdge SC servers.

PowerEdge Expandable RAID Controller, dual channel, integrated. An integrated solution, the PERC4/Di is dual-channel with a 320MB/second transfer rates. The controller has internal connectors and supports RAID levels 0, 1, 5, and 10.

PowerEdge Expandable RAID Controller with integrated mirroring. This embedded solution provides RAID Level 1 only, with one channel for mirroring on internal SCSI drives. It is a cost-effective, easy RAID solution.

PowerEdge RAID controller, single channel. The PERC4/SC is a single channel, 64-bit, 66-MHz card with 64MB RAM cache that supports RAID levels 0, 1, 5, 10, and 50. It is a PCI card qualified with one internal connection to support PowerEdge SC servers.

RAID Controller
The RAID controller, also referred to as the SP, is a Fibre Channel bridge controller between the HBA and the RAID disk storage array. Fibre Channel RAID storage can be configured in a single-loop or dual-loop configuration. Performance, availability, and configuration flexibility are inherent qualities of dual-loop configurations. The physical disks are shared between the dual SPs. Up to 120 hard-disk drives can be attached to each SP.

RAID-0 - Striped Disk Array
With striping, data is divided across multiple disks (or spindles). Data is broken down into blocks, and each block is written to a separate disk. The workload is reduced for all disks, helping to accelerate data delivery times. RAID-0 helps make disks more responsive, especially for e-mail, database, and Internet applications. RAID-0 requires at least two hard disks to implement. Advantages: Greatly improved performance by spreading the I/O load across many disks and easy to implement. Things to consider: RAID-0 offers NO data protection and should not be used for critical data.

RAID-1 - Mirroring
RAID-1 is achieved through what is called disk mirroring, and is done to ensure data reliability. The same data is copied and stored on different disks. If one disk fails, the data is available somewhere else in the array and can be easily restored. Mirroring not only creates redundant data for high availability, but keeps critical applications running as well. Advantages: Increased performance for reading data, with the same write performance as a single disk. 100 percent data redundancy means there is no data rebuild in case of a disk failure - simply copy the data from the remaining disk in the pair. Things to consider: Inefficient use of disk capacity-subsequently has the highest overhead of all RAID types (100 percent).

RAID-10 - Striping of Mirrored Arrays
RAID-10 is a combination of RAID-1 and RAID-0. This configuration requires at least four disks, and offers the best performance, protection, and capacity of all the RAID levels. RAID-10 consists of pairs of mirrored disks whose data is striped across the entire array. In many cases, RAID-10 can sustain multiple simultaneous disk failures making it less susceptible to downtime. It has the highest probability of no data loss. Advantages: Same redundancy as RAID-1 (mirroring) and is the best choice for data protection. Things to consider: Can be expensive, due to the mirrored disk array.

RAID-5 - Striping with Distributed Parity
RAID-5 maintains data redundancy through a technique called parity checking. As data is striped across multiple disks, parity bit data is included and also distributed among all the disks in the array. Parity is used to maintain data integrity and rebuild lost data in case of a disk failure. If one disk in the array fails, the missing data can be reconstructed from the remaining parity bits on the surviving disks. A RAID-5 configuration requires at least three disks. Advantages: Most efficient use of disk capacity of all the redundant RAID configurations and maintains good read-write performance. Things to consider: Disk failure can impact throughput rates and reconstructing information after a disk failure takes longer than with a mirrored configuration.

RAID-50 - Striping of Distributed Parity Arrays
RAID-50 is a combination of RAID-5 and RAID-0. This configuration stripes data with parity across each RAID-5 subset of disks. Each RAID-5 subset requires three hard disks. RAID-50 provides a higher degree of fault tolerance since one disk per subset may fail without data loss. Since the parity bits are distributed across the RAID-5 subsets, data rebuild speed is increased. Advantages: Greater degree of fault tolerance and potential for faster data read rates. Things to consider: Disk failure impacts throughput and reconstruction of information after a disk failure takes longer than with a mirrored solution.