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"200GB Hard Drive"

£200 plus vat though

http://www.ebuyer.com/customer/products/index.html?a ction=c2hvd19wcm9kdWN0X292ZXJ2aWV3&product_uid=43707

(remove space at end of first line)

Thanks for all the RAID info guys :).

Does anyone need that much memory tho, i know we will do in future,but not for at least a year. i suppose 200gb is good value for 235 quid,thats £1.20 per gb, if u look at a 40gb hard drive,it could cost up to 90,thats about £2.10 a gb
Sorry about me getting all mathematical

RAID arrays are effectively a cluster of disks all controlled to appear to, say, an operating system as one disk. The operating system reads and writes to the array without a care in the world that it's not just a hard drive, and the RAID controller (usually a bit of hardware either on your board or plugged into a PCI slot) takes care of the messy end. RAID, as someone else said, stands for Redundant Array of Inexpensive Disks - typically all disks in a RAID array will be the same capacity and brand, you may run into problems if they are not.

There are 3 main forms of RAID, which are RAID 0 (striping), RAID 1 (parity) and RAID 5 (striping with parity).

RAID 0 - in a normal disk, the file system is contiguous - that is to say, block one is first, block two is second, so on and so forth. Should a file occupy 10 blocks, then the disk can quite speedily read blocks 1-10 and give them to the operating system. In a RAID 0 array, block 1 is stored on disk 1, block 2 is stored on disk 2, block 3 on disk 1 again, block 4 on disk 2 and so on. This means if the same 10 block file was located on a RAID 0 array, it would be read by two disks reading 5 blocks each. RAID 0 can read/write at up to almost double the speed of a single disk, although in practise it's not much faster as most of the time the disks are seeking, rather than reading/writing. For large files, it makes quite a difference though. The only drawback is the data becomes twice as volatile - should either disk break, then all the data is lost.

RAID 1 uses the power of multiple disks for security, not speed. It is literally reading and writing to two disks at once - should one disk fail, the other disk contains a perfect copy, and the first can be easily rebuilt from that image. The disadvantage is that it's a bloody waste of disks, and is ever-so-slightly slower than a single disk.

RAID 5 is the best of both worlds, but requires a better RAID controller than you'll find on most motherboards. RAID 5 stripes data across many disks (block one on disk one, block two on disk two, block three on disk three, block four back on disk one etc), but reserves one disk for a parity check. All data is boolean - 1 or 0. Consider the following example of 6 hard disks that can only store 8 bits each, with one for parity:

Hard Disk #:
1 | 2 | 3 | 4 | 5 | parity
---------------------------
0 | 0 | 1 | 0 | 1 | 0 (0+0+1+0+1 = 0)
1 | 1 | 1 | 0 | 1 | 0 (1+1+1+0+1 = 0)
0 | 0 | 1 | 0 | 0 | 1 (0+0+1+0+0 = 1)
1 | 1 | 0 | 0 | 0 | 0 (1+1+0+0+0 = 0)
0 | 1 | 0 | 1 | 1 | 1 (0+1+0+1+1 = 1)
1 | 0 | 1 | 1 | 0 | 0 (1+0+1+1+0 = 0)
1 | 1 | 1 | 0 | 1 | 0 (1+1+1+0+1 = 0)
0 | 1 | 0 | 0 | 1 | 0 (0+1+0+0+1 = 0)


For each stripe (row in the table), the parity bit is the sum of the data bits in that stripe. In effect, it's like each row forms a sum, with the numbers making up the sum being the data bits and the answer being the parity bit.

This is clever because should you lose one of the disks, for each row you can reconstruct the missing digit. You either know all of the rest of the numbers and the answer (so can work out the value of the missing bit), or you've lost the parity disk, which can be reconstructed with ease. So not only do you get the recovery abilities of RAID 1, you also get the striping of RAID 0. The only drawback is that you lose one disk's worth of storage capacity, and you need an expensive controller to keep all this in check.

Another thing if you do buy this hard drive or anything over 120gb then windows will not see it as it's actuall size you can use intel application accelerator for intel motherboards, havnt needed to do it for any other.

c.b.

cjh wrote:
> 'RAID array'.
>
> What is one of those?

Raid (redundant array of independent disks) basically it is a way of storing the same data in differant places, thus redundantly.

Section copied from my self tutoring coursework.

RAID-0. This technique has striping but no redundancy of data. It offers the best performance but no fault-tolerance.
RAID-1. This type is also known as disk mirroring and consists of at least two drives that duplicate the storage of data. There is no striping. Read performance is improved since either disk can be read at the same time. Write performance is the same as for single disk storage. RAID-1 provides the best performance and the best fault-tolerance in a multi-user system.
RAID-2. This type uses striping across disks with some disks storing error checking and correcting (ECC) information. It has no advantage over RAID-3.
RAID-3. This type uses striping and dedicates one drive to storing parity information. The embedded error checking (ECC) information is used to detect errors. Data recovery is accomplished by calculating the exclusive OR (XOR) of the information recorded on the other drives. Since an I/O operation addresses all drives at the same time, RAID-3 cannot overlap I/O. For this reason, RAID-3 is best for single-user systems with long record applications.
RAID-4. This type uses large stripes, which means you can read records from any single drive. This allows you to take advantage of overlapped I/O for read operations. Since all write operations have to update the parity drive, no I/O overlapping is possible. RAID-4 offers no advantage over RAID-5.
RAID-5. This type includes a rotating parity array, thus addressing the write limitation in RAID-4. Thus, all read and write operations can be overlapped. RAID-5 stores parity information but not redundant data (but parity information can be used to reconstruct data). RAID-5 requires at least three and usually five disks for the array. It's best for multi-user systems in which performance is not critical or which do few write operations.
RAID-6. This type is similar to RAID-5 but includes a second parity scheme that is distributed across different drives and thus offers extremely high fault- and drive-failure tolerance. There are few or no commercial examples currently.
RAID-7. This type includes a real-time embedded operating system as a controller, caching via a high-speed bus, and other characteristics of a stand-alone computer. One vendor offers this system.
RAID-10. This type offers an array of stripes in which each stripe is a RAID-1 array of drives. This offers higher performance than RAID-1 but at much higher cost.
RAID-53. This type offers an array of stripes in which each stripe is a RAID-3 array of disks. This offers higher performance than RAID-3 but at much higher cost.

c.b.

Turbonutter wrote:
> Er mate that's £235.

£240.59 including P&P

oooh, i've got 3 IDE sockets, I could have 1TB and a CD drive...I don't feel like spending £1000+ for the privilage though.

'RAID array'.

What is one of those?

200GB is getting silly. If you have the need for that sort of capacity, you're probably better off with a RAID array. Mate of mine has a 900GB RAID5 array made up of 6 180GB disks, if any one of them fails he loses nothing.


Then a power spike hit his house and knocked out 2 of them at the same time |o/ He got the data back, but it took him a couple of months. Then he went out and bought an £800 UPS :O)

Er mate that's £235.

NIce drive though.