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FlashDisk Technology Backgrounder

Introduction
Speed is a key design goal of FlashDisk RAID Arrays and nicely complements its high availability. The industry is driving towards ever-faster servers-and FlashDisk is leading the drive towards ever-faster disk arrays. After all, why buy a server with 100 times more processing power if you just bottleneck it with a slow mechanical disk device? With controller-based caching, FlashDisk reads and writes data at electronic speeds. With FlashDisk, you improve overall server performance dramatically and then you can actually achieve the return on your server investment that you expected. Here's how:

FlashDisk Speed
To make a disk controller fast, three key elements in the array controller design must all be included:

• Fast hardware
• Efficient caching algorithms
• Multitasking architecture

Flashdisk addresses all three of these key elements and thus is able to produce these peak performances:

• Over 9,700 I/O operations per second
• 50 MB per second sustained data transfer rate

Technology Overview
FlashDisk arrays offer controller-based caching which eliminates host overhead found in low cost software-based caching schemes. Since FlashDisk provides all its own processing power, memory and algorithms, all disk activity is host independent and performed in parallel with host server operations. This architecture is key to overall application performance. FlashDisk issues immediate write completion notices to the application while the disk array completes the actual write operation. Read cache is fulfilled from memory at electronic speed rather than the mechanical speed of the disk drive. Thus for both reads and writes, FlashDisk multiplies the speed of your applications and the overall value of the server. Application benchmarks on FlashDisk versus standard SCSI disks are often two to ten times faster.

• High speed hardware

Data transfer through the controller is only as fast as the slowest link-so FlashDisk uses only high performance components.

• High speed internal PCI bus

FlashDisk employs a zero wait state, 133 MB per second PCI bus to transfer data to and from the internal memory to the SCSI controllers.

• High speed EDO RAM memory

Fast memory is important too. That is why FlashDisk uses zero wait state, 128 MB per second EDO RAM to store cache data and program algorithms. These memories are 40% faster than traditional RAM.

• High speed SCSI controllers

No matter how fast the internal controller and caching algorithms, the data must get to and from the controller over the industry standard SCSI bus. The turnaround time on this bus is critical, as a slow chipset here would completely limit the overall data throughput. Fast-wide differential SCSI host connections deliver up to 40 MB per second and Ultra-SCSI host interfaces deliver up to 80 MB per second data throughput.

• High speed parity calculations

Parity calculations can take too long if performed by the internal processor. Instead, FlashDisk includes a special hardware XOR chip to speed the processing of the parity information and it enables the controller to deliver an extremely high sustained data throughput.

• Single/Dual Ultra-SCSI Host Channels

The job of getting data to and from your host server is a paramount task-and FlashDisk delivers up to 50 MB per second data transfer rates by using an Ultra2, LVD SCSI host connection. You can use single-ended Ultra-SCSI for smaller arrays and simplicity of connection or differential Ultra-SCSI for multiple, daisy-chained RAID arrays and longer connection distances. Many FlashDisk models offer up to four host connections which can be connected to a single host to increase overall data transfer rates or up to four separate hosts to share the RAID array hardware or provide failover protection.

• Ultra-SCSI Disk Channels

FlashDisk RAID arrays come with either two or three Ultra-SCSI disk channels. These channels support Ultra Wide SCSI disk drives with disk-to-controller data transfer rates of up to 40 MB per second per disk drive.

• SCSI 2 Disk Drives

FlashDisk offers 10,000 rpm SCSI 2 disk drives, with seek times in the 5 msec. range. To some extent, the random I/O performance and data transfer rates depend more on the speed of the controller than the actual disk drives due to the benefits of caching. However, FlashDisk delivers the best overall random and sequential performance with over 9,700 I/O per second and 50 MB per second data transfer.

• Multitasking firmware architecture

FlashDisk is specifically designed with a multitasking firmware architecture to handle the demands of today's high speed, multiple client, multi-process servers. This architecture is key to its concurrent processing of multiple I/O requests simultaneously.

• Intelligent read-ahead cache

FlashDisk is designed specifically for multitasking servers. Its intelligent read-ahead algorithms support multiple threads of sequential data. These threads originate from multiple clients or from multiple processes initiated by each client.

• Intelligent write-back cache

Before writing to physical disk drives, FlashDisk reorganizes write operations to minimize physical drive I/O operations and thus minimize the overhead due to RAID parity updates. Further, sectors that are updated frequently, such as directories, may be updated again while still in cache. These sectors are physically written to disk only once, completely eliminating a portion of the I/O workload for many database and on-line transaction processing applications.

• Multiple RAID arrays

For larger departmental and enterprise size requirements, use multiple FlashDisk RAID arrays to multiply the I/O capabilities available to your server. FlashDisk RAID arrays are inexpensive enough to use liberally within your storage environment. You can stack up to 9 rackmount enclosures into a single data center cabinet for a combined total capability of up to 88,000 I/O operations per second and up to 450 MB per second data throughput for one large server or, more likely, for many servers to share.

Summary
FlashDisk RAID supports a variety of RAID features including multihosting and clustering. However, speed is a principal design goal of FlashDisk - hence the emphasis in the product name. To achieve this goal, the highest performance, mutitasking algorithms are executing on the highest speed hardware to deliver industry leading I/O performance for workgroup, departmental and enterprise class servers.

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