kiera mitchell

Capacity, reliability, and performance are important for file servers or other machines where you’re storing large or important files. Disk drives are vulnerable to failure, though, and when they do fail, data written since the last backup is lost. Disks have limitations on how fast they can go, although disk speed is only a limitation for heavily loaded servers.

What is RAID?
You can get much greater capacities, avoid losing data from disk failure, and do all that at reasonable cost using a technology called Redundant Array of Inexpensive Disks (RAID), invented at the University of California at Berkeley by D. A. Patterson, G. Gibson, and R. H. Katz. The industry also uses the phrase Redundant Array of Independent Disks, so you’ll probably see both. RAID uses conventional disks with specialized host adapters to change how data goes onto your disk.

What RAID Does
The idea behind RAID is to take the conventional disks in personal computers and gang them together in parallel. The resulting assembly gives you the low cost of disks manufactured in high volume plus good reliability and a multiplier on the performance of individual disks.

The host adapter (frequently called a controller in RAID systems) sits between one high-rate data stream (on the computer side) and several lower-rate streams (on the disk side). When the computer writes to the disk, the host adapter takes high-rate data and breaks it into multiple synchronized streams, one for each disk, in a process called striping. Reads by the computer cause the host adapter to take a data stream from each disk, multiplex the set of streams into one stream, and send that resulting stream on to the computer.

In the example shown below, the one high-speed stream splits into four separate disk data streams at one-fourth the rate of the combined stream.

There are six different levels of RAID functionality. The simplest RAID system, RAID level 0, merely stripes the data onto multiple disks for better performance. There is no overhead for redundant data storage and no protection against failure. The highest level is RAID 5, which provides both striping for performance and redundancy for failure protection.

RAID Level 0
RAID level 0 spreads the data stream across multiple disks. You can get a similar effect to that of RAID 0 by having multiple disks and can use features in Windows 2000 or Windows XP to simulate RAID in the operating system. Suppose your computer sends a sequence of data to a RAID 0 host adapter connected to two disks. The host adapter will interleave the data to the two drives, sending odd blocks to one drive and even blocks to the other.

Because the data volume and rate to any specific disk is a fraction of the aggregate, you get better capacity and performance from RAID 0 than from a single conventional disk. There is no error correction or redundant data written to the array, however, so RAID 0 cannot survive a disk failure. You would use RAID 0 only in situations where you needed the capacity or performance gain, but not the enhanced data reliability.

RAID Level 1
In the same way that RAID 0 focuses solely on capacity and performance with no concession to reliability, RAID 1 focuses on reliable data storage with no concession to capacity or performance. RAID 1, also called disk mirroring, uses disks in pairs with both disks of a pair storing the identical data. The redundant copy protects your data against hardware failures, but you’re still vulnerable to user error deleting important files.

Suppose your computer sends a sequence of data to the RAID 1 host adapter connected to two disks. The host adapter will write all the data to each of the two drives. The identical data is stored on both drives, so if one fails, the data is still available. The operation completes when both drives have written the data, so the write can take longer than for one disk alone because of delays for unsynchronized rotation and for I/O bus contention.

RAID 1 offers better reliability than RAID 0 or conventional disk setups, but does not increase performance.

RAID Level 2, Level 3, and Level 4
RAID 2 adds one or more disks to hold an error correction code with which lost data from a failed disk can be reconstructed. When your computer sends a sequence of data to a RAID 2 host adapter connected to two data disks and an ECC disk, the host adapter interleaves the data to the two data drives. Odd blocks go to one drive, and even to the other. The host adapter computes the error correction code for the data written to the data drives and writes it to the ECC drive.

RAID 3 is the same as RAID 2, except that it uses a simpler code — parity instead of ECC. RAID 3 has the same small-transfer performance limitations of RAID 2, but less storage overhead.

RAID 4 is nearly the same as RAID 3, but instead of striping across disks at the byte level, it operates at the sector level. This makes RAID 4 like RAID 2 except that it uses parity rather than ECC, and it interleaves sectors. RAID 4 therefore has good data reliability and storage efficiency, as do RAID 2 and 3, and retains fast writes for large data blocks.

RAID Level 5
RAID 5 is the same as RAID 4, except that instead of dedicating a single disk to storing parity, the parity data stream is striped across all the disks along with Suppose your computer sends a sequence of data to a RAID 5 host adapter connected to four disks. The host adapter interleaves the data to the drives, ensuring that no one drive ever holds two blocks of a group protected by a parity block.

The host adapter inserts the new parity information in the data stream that it sends to the disks, mixing the parity information in with the original data. As long as there is at least one more disk than there are original data streams, the loss of a disk can take out only one data stream, and so parity is enough to regenerate the lost data.

Conclusion
RAID technology can be difficult to understand, especially for the beginner. Do go through the above tips to understand it so that you can make better purchase decisions when building your next computer system.

Gary Hendricks runs a hobby site on building computers. Visit his website at http://www.build-your-own-computers.com for tips and tricks on assembling a PC, as well as buying good computer components.

Yeeeah… That’s A Problem

You just got paid and it’s time to get that new laptop you’ve been dreaming of. So you head off to the store, pick up your new (insert brand name here) laptop and bring it home to check out your spoils. You’re thrilled when everything works great, until you try to plug in your cellular internet PCMCIA card. Then you realize that the card won’t fit! What’s to be done?

ExpressCard Muscling In

This is a scenario that is becoming more and more common as computer manufacturers roll out new laptops using the newer, faster ExpressCard standard. And along with the advent of this new technology comes the demise of the PCMCIA standard, which will become more and more rare. Although the ExpressCard offers significantly faster speeds and a more compact form, which will help to keep laptop design slim, the rapidity of the rollout has caught ExpressCard manufacturers struggling to keep up with demand as consumers seek ExpressCards to replace their existing PCMCIA cards. Perhaps the most prevalent issue is that while there are now ExpressCard versions of most PCMCIA cards, there are few, if any, viable alternatives for EVDO, EDGE, or GSM cellular internet PCMCIA cardbus cards.

EVDO Wireless Router

There are several potential solutions to this issue. The first would be to buy a specially designed stand-alone router with a cardbus slot specifically intended for a wireless internet card. This router takes the cellular signal from the aircard and converts it into a WiFi signal that can be picked up by a standard 802.11b/g wireless adapter. The 3G Phoebus is in this class of router.

ExpressCard to PCMCIA

Another solution is to use an ExpressCard to PCMCIA adapter. This adapter plugs into your available ExpressCard slot, and allows you to connect your wireless aircard (via an attached cable and receiver) to your laptop.

USB to Cardbus Adapter

The best available solution for this problem is to use a USB to PCMCIA adapter. This adapter consists of a USB cable that is attached to an adapter that is designed to allow you to insert your cellular PCMCIA card. Simply plug the USB port into your computer and do a simple install to take advantage of wireless internet with your new ExpressCard laptop.

Nate Kartchner is the Marketing Coordinator for Sewell Direct, a premium online retailer specializing in hard-to find adapters and connectivity solutions like the 3G Phoebus and the USB to Cardbus Adapter.

Entry level printers can mean a lot of things for the average user. Some would say that entry level printers are in a class of affordable machines for start up users. Another segment may say that entry level printers should be easy to use and should not scare away a potential power-user. These qualities are true for budding professional photographers and office managers. Therefore, this cool list of starter sums the best get-to-know-me printers.

HP Photosmart C5280 Multifunction Printer

If you are on a tight budget, the HP Photosmart C5280 Multifunction Printer is a great do-it-all printer for you. The clean white printer dishes out professional photo prints and great color scan quality, which is a combination that higher end printers should also bring. It also prints at a lower cost per page, and with the Roxio label printer, home users can create their custom CD labels from their HP Photosmart C5280 Multifunction Printer. Its stock of printer inks such as HP #74 ink (CN335WN) also features high yield printing. While you might experience diminished text quality, and while the photo menus need a revamp, the HP Photosmart C5280 Multifunction Printer excellent graphic printing judged against its cost makes it a nice match for the casual home user.

Canon Selphy CP740

The Canon Selphy CP740 is a perfect entry level photo printer used for a variety of task at a highly acceptable quality. The white light box is compact enough to be carried in a tote bag or a large purse. At 2.1 pounds, you can carry the Canon Selphy CP740 anywhere. The main praise for Canon Selphy CP740 is its ease of use and low cost for people who want to take various snapshots and get their print outs quick. The Canon Selphy CP740 is a nice companion for the simple in and out printer that does not complicate much.

HP Photosmart A826

If you can shell out some money, you will be delighted with the ease of using the HP Photosmart A826. The little blue box looks straight out from a spaceship as with its trapezoid shape and blue lid. The large touch screen can be used to display slide shows while the menus are organized so that anyone can get a printing job done without opening the manual. If you can bite the price, the trade-off with its ease of use and quality prints from the HP Photosmart A826 makes it a fair buy. Replacement printer ink cartridge also dampens your printer cost as long as you buy discount HP 110 (CB304AN#140) printer ink cartridges.

Canon Pixma iP1800

The Canon Pixma iP1800 printer is a bare bones printer that does the most basic things while it charges you at a modest price. For $50 can get a useful printer equipped with a paper feeder, a dual printer ink cartridge system, and a USB port for universal connectivity. The Canon printer ink cartridge replacements are not that pricey with remanufactured Canon CL41 for color printing and the Canon PG40 for black printing.

If you look at it purely as an entry level printer, the Canon Pixma iP1800 will definitely not disappoint. However, you won’t get an output tray for its price but it does the starter things very well and will be a good standard for your next printer needs.

This Article is written by James Kara Murat from PrintCountry.com, the contributor of PrintCountry Ink & Printer Reviews. Read more about the subject at Best Entry Level Color Laser Printers of 2007, and related resources can be found at PrintCountry FAQ.

Welcome to Blogsplace.info. This is your first post. Edit or delete it, then start blogging!