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Fast and Inexpensive - Promise
Краткое содержание статьи: With a very small 'operation' you can modify a Promise Ultra66 controller into a FastTrak66 ATA RAID-controller and benefit from its high performance. We put this self-made device to the test.

Fast and Inexpensive - Promise's FastTrak66 IDE RAID-Controller


Редакция THG,  29 марта 2000
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RAID 1 - Mirroring

RAID 1 is also called 'mirroring', because it simply keeps a complete copy of one drive on another drive. A RAID 1 array of two hard drives has the storage capacity of only one drive, because the other drive contains the 'mirror'. RAID 1 is obviously the most reliable kind of array, because it always keeps a complete backup of your data. Its performance is naturally not as high as RAID 0 though. Read requests are actually faster than from one single drive, because the data is simply read from the one drive of the two that delivers it faster. RAID 1 is therefore reducing the access time. Write requests are usually slower on RAID 1, because the data needs to be written on two drives and then compared.

RAID 1 is usually offering 'hot swap', which means single drives in the array can be removed or replaced while the system is running, without interruption. However, once one drive in the array has failed, you need to replace it to ensure data integrity, and if you replace it with a new drive, this one needs to be 'filled' with the mirror again. This has naturally an impact on the performance of the array until the mirroring is finalized.

As you can imagine, RAID 1 is not only a very secure, but also a rather expensive RAID-solution, because you need two hard drives for the capacity of only one.

RAID 10 or 0,1

This RAID level resembles a combination of RAID 0 and RAID 1. The idea is to mirror a stripe set or to stripe a mirror. The effect is the same. Due to striping, the read and write performance is excellent, as long as no failed drive needs to be rebuilt by the mirror-process. The reliability is also excellent, because you still have a complete backup of your data on another drive. However, you require double the amount of drives than with RAID 0 to achieve the same capacity.

Spanning

'Spanning' is no RAID level, but it is another option offered by the FastTrak66. It simply makes one drive out of a number of drives, regardless of their size. It does neither stripe nor mirror, but it simply hangs one drive on another, so that e.g. a 13 GB and a 8 GB drive make one 21 GB drive. Data stored on this 'spanning-array' is first stored on the first drive and when this drive is full the next data goes onto the next drive. The performance in each dedicated 'area' of the span-array is identical to the performance of the single drive that represents this area.

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СОДЕРЖАНИЕ

Обсуждение в Клубе Экспертов THG Обсуждение в Клубе Экспертов THG


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