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FREQUENTLY ASKED QUESTIONS
1. Do your units support the latest 2TB SATA II hard drives? 2. What are the transfer rates/speeds of different connections?
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USB2.0
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480 Mbps
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Firewire400/IEEE1394a
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400 Mbps
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Firewire800/IEEE1394b
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800 Mbps
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SATA I
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1.5 Gbps
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SATA II
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3 Gbps
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SCSI U320
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320MBps
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Fiber Channel
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2/4Gbps
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RAID stands for "Redundant Array of Inexpensive Disks". The concept of RAID originated from a paper ("A case for Redundant Arrays of Inexpensive Disks" - 1987) published from the University of California at Berkley, proposing that using multiple small and rather inexpensive disks to replace the use of a single large disk to achieve fault-tolerant data redundancy. Another term "Parity Data" was often mentioned together with RAID. The parity data or disk is used to reconstruct data to a failed drive by comparing the data for the remaining drives in the array.
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Originally five RAID configurations, levels 1 through 6, were defined. A newer version, "data striping", or level 0, offers some performance advantages over other RAID levels but no data redundancy, so technically it isn't actually RAID. The most popular RAID levels are 0, 1, 3, 5 and 6, their definition of RAID levels are:
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RAID 0 |
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Known as disk striping. High Performance but no protection. It combines disks into one RAID that are used to improve some performance, but there is no logic to protect/recover data. *Synchronized disks are used.
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RAID 1
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This is known as mirroring. Data is written to two different disks at the same time, and data can be read from either disk. This helps to protect the data. If one disk is defective, the unit can still read the data from the other disk.
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RAID 3
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Striping data over several disks. Provides performance and protection. One of the disks will be used as parity. Parity interleaves at byte level and is stored in a dedicated disk. *Synchronized disks are required.
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RAID 5
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Striping data and parity over several disks with no dedicated disk for parity.
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RAID 6
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For each data stripe, there are 2 different and separate parity bits stored on 2 different disks among the RAID array members. There are 2 separate hardware XOR engines to generate the 2 parity bits. There are 2 major reasons justifying the need for RAID-6.
* Synchronized disks - Multiple disks are being used to write a single file. This is a function of the disk controller.
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JBOD stands for Just Bunch Of Disks. A group of disks configured in an enclosure that are not configured as a RAID for fault-tolerance. There is no redundancy of the hard drives (No-RAID) and there are just bunch of disks in the enclosure. The simplicity of JBOD makes it a good choice to increase the capacity of the system easily and economically.
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