Drive Arrays JBOD (Just a Bunch Of Drives). Drives used individually. For example you put OS and Programs on one, you audio on another, and your photos on a third. Some folks use this, mistakenly, for the next.
Concatenated Drives. Drives connected end to end. When drive one is full data is automatically written to drive two and so on. The advantage is you can keep adding drives as you fill them. This has been available on the OS at least since DOS-5. Actual RAID ARRAYS are seen as a single large drive by the OS: RAID-0. (N-drives) any number of drive connected in parallel so that data is written, and read, across them. A simplified way of thinking of it is to imagine a large many sector file. The first sector would be written to drive one, the second to drive two, the third to drive three and so on until you get to the last drive in the array and then the next sector is written to drive one and you are starting over. So you can see that if any drive fails you lose the whole file because there are large chunks missing from it. The advantage is that the raid controller can write across all those drive almost simultaneously so it can be very fast. If you have critical data on it you need a truly rigorous backup system. RAID-1. Mirrored drives (N+N drives). The entire data set is written to two or more drives simultaneously, so you automatically have two or more copies of the data. This give the maximum redundancy of any of the RAID methods, but you should still back up your data off-line. RAID-5 This is an N+1 array any one drive can fail without loss of data. The easiest way to imagine how it works is to go back to that large file used in the RAID-0 explanation. However in RAID-5 each sector is written to two drives. For example sector one is written to drive ones and three, sector two is written to drives two and four, etc. Since any one sector is always written to two drives the array can easily be rebuild if one drive fails, you can also add drives easily with most controllers thus meeting increased data needs, also you only need one extra drive. It is midway between RAID-0 and 1 in speed and redundancy. Those are the most used arrays. Most of the others have some limitation or are combinations of these, for instance you can mirror RAID-0, or RAID 5 arrays. RAID-1 and RAID-5 give some protection from common drive failures. None of them protect you from bad data. None of them protect you from catastrophic system failures. Backup your data. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
