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Friday, December 16, 2011

Setting up 2 Hard drives using RAID ,What is RAID

Subject: Setting up 2 Hard drives using RAID
I have a large amount of music (~80GB) and digital pictures, along with a lot more that I could not bare to lose, on my computer. I currently have 2 120GB Western Digital Caviar hard drives. Only one is in use currently. I backed up everything I had to the other a few
months ago. I am looking for a way to have both hard drives connected at the same time, containing exactly the same data on both, so as to have a backup if one fails. I've heard of something called RAID which would let me do this, but I want to know how exactly I can accomplish this (what i need to buy and how to set it up) and what my options are. It occurs to me that writing the same data on two drives would slow things down. Is there any way around this? I am runnning:
Windows XP Pro
ASUS A7A266 Motherboard
AMD Athlon 1.4 Ghz
2 120GB Western Digital Caviar Hard drives
Antec 400W Power supply

: Setting up 2 Hard drives using RAID
As you've gathered, a RAID setup will allow you to clone your hard drives, thereby creating redundancy in your data in case one of the drives should fail. There are various different RAID levels, each with different advantages and disadvantages, but I don't think it's
necessary to dig in to the details here. If you want to read up on all the RAID levels and how they work

In your case you want to set up a disk mirroring system. Everything that gets written to one drive gets written to the other drive at the same time. This is RAID Level 1. It requires that you have two drives of the same size connected to a RAID controller. This card is
nothing more than a special IDE controller. Good entry level controllers are available from Promise, and should sell for under $100. One site with a well-reviewed Promise card, capable of ATA133
but obviously there are many retailers for such cards. I've had very good experiences with Promise cards in the past, though cards are also available from manufacturers like Adaptec and 3Ware. In your case the Promise cards will be perfectly suitable and probably the cheapest way to go.

Installation of these cards is really very simple. You'll need to install the controller into an empty PCI slot, then boot Windows and install the driver for the card (the exact procedure depends on the card you purchase). Once that's done, disconnect the hard drives from
the IDE connectors on the motherboard and connect them to those on the RAID controller.

Setup varies from card to card, but generally configuration is accomplished by hitting a key combination at boot time and going through menus. You'll configure the attached drives just like you would in the motherboard BIOS setup, and then you should find an
option to create the array. Again, the exact procedure varies from card to card, but after establishing how you want the array to work (for instance, which is the source of your existing data and which is the empty drive to which it should be copied) the drives will be
mirrored. When you reboot, the RAID controller will take care of all your data access and will mirror your information without you having to think about it. There should be no noticeable performance hit. In fact, because it's able to read from two drives at once, on some
things you'll actually notice a speed increase.

It's really not a difficult task, and if you are comfortable doing basic computer hardware work you'll be just fine. If not you should probably take it to a computer shop to have it done. I hope this proves useful to you. Let me know if you need any clarification.

Good luck,

However, I am still fuzzy about one thing. Since I have data on both drives, how do I go about hooking them up to the RAID controller? I really do not want to risk losing the data. Would I have to format the backup drive before I connect them both to the RAID? What will
happen to the data? Also, about purchasing the RAID card, I have looked on
www.pricewatch.com, and , under I/O >> Controller Cards, I see a category for "RAID" and one for "Array RAID", with prices in the "RAID" category starting at $17, and in the "Array RAID" category starting at around $62. Now I do not want to get something of bad quality, but I do not want to spend too much money if it is not necessary. I even see Promise RAID cards starting at $60. What advice could you give on what card to buy?

I think I misunderstood how your data was stored. You will need to clear the data off one of the drives in order to create the mirror. Any data that gets mirrored on the drive will overwrite what exists there now. So before you plug in the RAID card you should transfer
all the data off your D: drive (for instance) on to C:. You probably won't need to format it first, but it might be necessary (the RAID controller might not want to allow you to overwrite data).

As for the categories on Pricewatch, I'm a bit puzzled. RAID setups are always arrays of drives, be it two, three, five, or however many drives in the configuration. My first thought was that maybe the controllers there could handle RAID 5, or perhaps two channels of RAID
1 (so four hard drives, two mirrors) but this also isn't the case. There also appears to be overlap between the two, since the same controllers that appear in the RAID category for $60+ also appear in the RAID Array category. It's very strange. However, I really wouldn't suggest opting for the cheapest option here. A $17 RAID card may work, but support for it will probably be horrible. You're best off sticking with a reliable brand with good driver and setup support. I would suggest Promise, Adaptec, LSI, or AMI. All of these have
been good to me in the past. Beyond that, make sure the controller you opt for has support for ATA133. An ATA100 interface won't use the full potential of your drives. Finally, if you're sticking to only these two drives (one mirror) you can go with a single channel
controller, but if you think you might add another mirrored set later you should get a two channel card. It looks like the cheapest card that meets all these specs is probably the Adaptec 1200A.
And finally, jumper settings are usually you're standard Master/Slave. If you've got the two drives working on the same IDE channel right now you shouldn't have to make any changes to the jumpers. The manual that comes with the card will tell you if it's otherwise.

RAID demystified
RAID is a technology that is quickly becoming more prevalent in the computing world today. What was once confined to the corporate world has now penetrated the home user market. You can hardly find a new motherboard these days that doesn't include some form of integrated RAID. So what is RAID and what is it useful for?
RAID stands for Redundant Array of Inexpensive Disks, and there are different types -- or levels -- of RAID which perform different functions and serve vastly different purposes. This article will cover the most common RAID levels: 0, 1, 5, and multiple arrays.
RAID 0
Also known as "striping," RAID 0 was designed to increase hard drive performance at the expense of fault tolerance. Hard drives of equal size and speed are combined in capacity and efficiency, decreasing hard drive read and write access times and improving overall performance. However, if one drive in the array should fail, all data would be lost.
In a RAID 0 array, data is written in 64k chunks to each drive, one after another. For example, if you have 3 hard disks in a RAID 0 array, the sequence for writing to them would go 1, 2, 3, 1, 2, 3, and so on. This reduces the overall strain on each single drive, which lengthens their lifespan and allows for high throughput speeds because multiple drives can be accessed simultaneously.
RAID 0 is usually used in desktop and workstation machines that require fast disk access time or large contiguous storage space.
Advantages: provides the best disk read/write access out of all the levels of RAID. Also reduces the strain on each individual hard drive.
Disadvantages: No error correction or fault-tolerance.
RAID 1
Also known as disk "mirroring" or "duplexing." Two hard disks of similar size and speed are required. Whatever is written to the first hard disk is simultaneously copied onto the second, so in essence you have two hard disks with the same data. The purpose of RAID 1 is twofold: it increases read times in multi-user systems because data can be read from either drive. It also is a failsafe against drive failure; if one drive should fail, the other will continue to operate normally.
RAID 1 is not as fast as RAID 0 in terms of write speeds because of all of the replication traffic generated -- it has to write the same data to two drives at once.
There is a small difference between mirroring and duplexing. Mirroring uses two disks on one controller using one cable. In this case, if the drive controller goes bad, the system goes down. Duplexing uses two disks on two controllers using two separate cables. If a controller fails, the system just switches over to the second hard disk and keeps on going. RAID 1 is often used to provide fault tolerance in entry level servers that aren't equipped for the more expensive and power-hungry RAID 5.
Advantages: provides fault tolerance and increased read times.
Disadvantages: slower write times than RAID0.
RAID 5
Also known as disk striping with parity. RAID 5 takes the concept of RAID 0 and adds fault tolerance. RAID 5 requires at least 3 hard disks to function. Data is written to each disk in the same fashion as RAID 0, but parity data for each drive is stored separately on other drives. In the event of a hard disk failure, a replacement drive can be added and the contents rebuilt from the parity data stored on the other drives. RAID 5 is often used in high-end servers that store mission-critical data. It's essentially one step below a dedicated storage cluster.
Advantages: more reliable fault tolerance than RAID 0 and RAID 1.
Disadvantages: more expensive, requires more disks and a more advanced RAID controller. Not quite as fast as RAID 0.
Multi Level RAID
You can also set up a RAID array that has multiple levels. This form of RAID is very expensive and is mostly found in large enterprise networks storing mass amounts of crucial data. A specialized RAID controller or external RAID device is normally required.
The most common implementations of this concept are RAID 10, 0+1, and 50. They are what they sound like: RAID 10 is a mirror of two striped arrays; 0+1 is a stripe of two mirrored arrays; and 50 is a stripe of multiple RAID 5 arrays. Several hard disks and a high-end RAID controller are required to form most of these arrays.
Advantages: fast read and write access with redundancy.
Disadvantages: expensive, requires at least four disks and a specialized controller card.
Different forms of RAID
RAID comes in two different forms: hardware level and software level. Hardware RAID is more expensive because it requires an advanced RAID controller such as those made by Promise, Highpoint, LSI Logic, and Adaptec. Hardware RAID controllers can also be built into the motherboard or housed in a separate, self-contained unit connected externally via a SCSI or network cable.
To administer your RAID array, you will invoke a specific keystroke during the system boot sequence -- usually a message appears briefly, telling you what key to press. This will lead to the RAID BIOS setup utility. Some companies also bundle a Windows-based application that allows you to administer your array through the operating system, where you can add, delete and modify an array.
The following are required for hardware RAID: A RAID controller corresponding with your hard disk type (ATA, SATA, or SCSI) or a network storage device. The controller can be a PCI or PCIe card, or an integrated solution built into the motherboard. Be careful! Many of the RAID controllers built into motherboards are not hardware RAID controllers; they are merely fancy drive controllers that facilitate software RAID arrays.
1. Minimum amount of hard disks for the type of RAID array you want to build.
2. A supported operating system. These include Windows NT/2000/XP Professional/2003, GNU/Linux, Free/Open/NetBSD, and Solaris, although there are many other OSes that could work. Make sure the OS you choose has a driver for the RAID controller.
RAID with software
Software level RAID is less expensive but not as fast as hardware level and is generally used as a less expensive alternative to its hardware-controlled counterpart. To administer a software array in Windows 2000 Server, go to the Control Panel, then open up Administrative Tools, then Computer Management, then Disk Management. In the lower right pane, right-click on the hard drives you wish to use in the RAID array and then click on Convert To Dynamic Disk in the popup menu. From there you can set up your array with relative ease.
For GNU/Linux and other Unix-like OSes, the answers on how to set up software RAID vary depending on what version and distribution you're using. More than likely you'll end up using the Device Mapper; a brief readme document on dmraid can be found here.
What you will need for software level RAID:
1. An operating system that supports software RAID (GNU/Linux; Free/Open/NetBSD; Windows 2000/2003 Server, Advanced Server, or Datacenter Server; and Solaris) and software to set up and manage the arrays.
2. Minimum amount of hard disks for the type of array you want to set up.
JBOD and Disk Spanning
A lot of people talk about JBOD and disk spanning as being considered forms of RAID. This is not really true; JBOD stands for Just a Bunch Of Disks and its purpose is to combine multiple hard disks into one. It does not provide redundancy, and therefore is not technically a level of RAID. However, JBOD is useful if you have an application that requires mass amounts of contiguous hard disk space and you don't have a large drive to use. This should only be used as a band-aid fix though, as several drives combined leads to increased chances of failure.
Disk spanning differs slightly from JBOD. With disk spanning you can actually administer the disk array, whereas with JBOD you just set it up and go. With disk spanning you can extend existing partitions onto other empty partitions or hard disks to gain extra contiguous disk space. This should also only be used as a band-aid fix because, like JBOD, disk spanning provides no redundancy whatsoever. If one drive in a JBOD or disk span array goes down, its data is lost.
A JBOD or spanned array requires a RAID or hard drive controller that supports these modes, and the hard drives to form the array. Setup is done through the controller's BIOS.
Is it right for you?
RAID is useful for providing expanded hard drive capabilities in desktop, workstation, and server machines. Most home users will only be considering RAID 0 or 1 because that is the usual limit of the integrated RAID chip on their motherboards, not to mention the fact that other RAID modes cost a lot of money in disks.
RAID 0 can be useful to people playing online games, doing video editing, or any other operation that can benefit from faster read/write times. Most budget-minded business users in search of fault tolerance can rely on the redundancy of RAID 1. The other modes and options aren't generally practical for desktop use and it's unlikely that you'll see any advantage to using them.

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