Dell Precision 490 Desktop User Manual

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segments—or stripes—of data sequentially across the physical drives to create a large virtual drive. Data striping allows one of the drives to read data whilethe other drive is searching for and reading the next block.Another advantage of a RAID level 0 configuration is that it utilizes the full capacities of the drives. If you have two 120-GB drives installed, you have 240 GBon which to store data.RAID Level 1RAID level 1 uses a data-redundancy storage technique known as "mirroring." When data is written to the primary drive, the data is then duplicated—ormirrored—on the other drive. A RAID level 1 configuration sacrifices high-data access rates for its data redundancy advantages.If a drive failure occurs, subsequent read and write operations are directed to the surviving drive. A replacement drive can then be rebuilt using the data fromthe surviving drive. Also, because data is duplicated on both drives, two 120-GB RAID level 1 drives collectively have a maximum of 120-GB on which to storedata.RAID Level 5RAID level 5 uses a data-staging storage technique known as "parity checking." When a block of data is written to the RAID configuration, it is striped acrossall of the drives in the RAID array except for one drive, to which is written parity data. The parity data is information that allows for the entire block of stripeddata to be calculated if one of the drives fails.Since parity data is fairly small when compared to the size of the actual stored data, the equivalent of one hard drive can serve as a parity drive for anynumber of data-storing hard drives. However, not all of the parity data is put on the same drive. Instead, with each new block of data written to the RAIDconfiguration, the different drives alternately act as either data-storing or parity drives.NOTICE: Because RAID level 0 provides no data redundancy, if one drive fails, then the data on the other drive is also inaccessible. Therefore, ensurethat you perform regular backups when you use a RAID level 0 configuration.