Subscribe to Windows IT Pro

 

Get Newsletters

  • Get the Latest News
  • Product Updates
  • Helpful Tricks
  • Productivity Tips

Subscribe Now!

August 01, 1997 12:00 AM

RAID-Related Terms

Joel Sloss
Windows IT Pro
InstantDoc ID #221
Rating: (0)

RAID depends on several technologies to make it work, including SCSI controllers and wiring schemes that RAID and SCSI controllers use. Here are definitions of these technologies. For more information about SCSI technology, see Sean Daily, "SCSI and IDE," June 1997.

SCSI Standards

SCSI-1 The original SCSI standard, offering synchronous (5MBps) and asynchronous (3MBps) modes. Supports single-ended configurations, with passive and active termination.
SCSI-2 The second standard, and the most common today. You can mix SCSI-1 and -2 devices on one SCSI-2 bus because it's backward-compatible to SCSI-1. SCSI-2 offers much higher burst and sustained transfer rates (although the standard is only 5MBps), with a clock speed of 20MHz.
Fast SCSI-2 Runs at 10MBps.
Wide SCSI-2 Runs at 10MBps but extends the data path to 16 or 32 bits.
Fast and Wide SCSI-2 Runs at 20MBps over a 16-bit data path.
SCSI-3 Also known as Ultra SCSI (or Fast 20). It is fully backward-compatible to SCSI-2 and uses 4-bit (deep) addressing. This new standard extends performance to 40MBps.
Fast SCSI-3 Runs at 20MBps; cable length limits are the same as SCSI-2,
unless you have differential wiring.
Wide SCSI-3 Runs at 40MBps. SCSI-3 is by nature "fast"; doublewide uses 32 bits instead of 16.
SCSI-4 Also known as Ultra 2. It is a 64-bit standard designed for 64-bit PCI and runs at 80MBps with a clock speed of 40MHz.
Deep SCSI Uses 4 bits instead of 3 to identify devices on the bus, allowing for up to 15 total devices on a channel.
Single-ended wiring Cable wiring scheme that is more prone to noise because all signal lines use a common ground. It has a 6-meter cable length limit.
Differential wiring Wiring scheme that uses signal/ground wire pairs, which reduces noise and allows for up to 25-meter cables. The two versions of differential are low-voltage (LVDS) and high-voltage (HVDS). The one you choose depends on the cable length you want, data speeds, and other factors­HVDS is for SCSI-4. You cannot mix single-ended and differential devices on the same bus.

Related Content:

ARTICLE TOOLS


Want to use this article? Click here for options!

Comments
Add A Comment
    There are no comments to display. Be the first one!
You must log on before posting a comment.

Are you a new visitor? Register Here

advertisement

advertisement

White Papers

Get your Windows 7 deployment off to the right start by implementing PC lockdown. A locked-down environment is easier and cheaper to support since users are less likely to make unnecessary changes to the core system configuration - read more here!

Essential Guides

Is your iSCSI "lossy"? The reality is that most off-the-shelf Ethernet hardware deployed for iSCSI can lose packets, resulting in slow performance or application downtime. Learn how to assess your current iSCSI infrastructure and engineer an advanced iSCSI SAN infrastructure.

Web Seminars

What's the best way to keep your network safe from malware? In this web seminar, security expert Greg Shields suggests an alternative method to the traditional blacklisting approach that is common with anti-virus and anti-malware solutions.

eLearning Series

We bring the experts direct to you to share their real-world perspective and expertise. During each event, three sessions stream in real time, so you can learn, ask questions, and get solutions.
Upcoming event: Getting the Most with Exchange 2010 with Paul Robichaux

Subscribe to Windows IT Pro!

Cloud IT Pro DevProConnections Left-Brain Mobile Dev Pro SharePoint Pro SQL Server Pro SuperSite for Windows Windows IT Pro

© 2012 Penton Media, Inc.

Home About Us Advertise Customer Service Privacy Statement Subscribe/Renew Terms Of Use

Windows is a trademark of the Microsoft group of companies. Windows IT Pro is used by Penton Media Inc. under license from owner.