Frequently Asked Questions
LaCie 4big Quadra RAID Modes
The LaCie 4big Quadra supports RAID levels 0, 10, Concatenation, 3, 3+spare, 5 and 5+spare. The following chart sums up the strengths and weaknesses of each RAID level.
The 4big Quadra is pre-configured in RAID 0, the fastest RAID mode. Requiring at least 2 drives, RAID 0 stripes data onto each disk. The available capacities of each disk are added together so that one logical volume mounts on the computer. If one physical disk in the array fails, the data of all disks becomes inaccessible because parts of the data have been written to all disks.
RAID 10 (also called RAID 1+0) is another RAID level that combines the attributes of other levels, specifically RAID 1 and RAID 0. It is a “mirror of stripes”, meaning that data is striped across two mirrored arrays. The Striping occurs between arrays and the mirroring occurs within the same array. In a RAID 10 array, one disk from each mirrored pair can fail with no data loss. However, the working disk in an array with a failed disk becomes a weak point for the entire array. If the second disk in a mirrored pair fails, the entire array is lost.
When disks are concatenated, their capacities are combined and data is written to the primary disk in the array until is it full, and then to successive disks. Concatenation provides no performance advantage or added measure of data safety. It is simply a method of combining more than one physical disk into one volume for greater overall capacity.Concatenation allows full use of the capacity of all disks in the array and most data can survive a disk failure. Only data on the failed disk and data that is partially written on the failed disk and an operative disk is lost.Offers the maximum possible capacity by combining the capacities of several drives into one large volume.
RAID 3 and RAID 3+Spare
RAID 3 uses byte-level striping with a dedicated parity disk (Disk 4 in the illustrations, right) so that one volume mounts on the computer. A RAID 3 array can tolerate a single disk failure without data loss. If one physical disk fails, the data from the failed disk can be rebuilt onto a replacement disk. If a second disk fails before data can be rebuilt to a replacement drive, all data in the array will be lost.In RAID 3+Spare, one disk in the array is left empty. If a drive in the array fails, the data from the failed disk is automatically rebuilt to the empty or “spare” disk.
RAID 5 and RAID 5+Spare
RAID 5 combines the striping of RAID 0 with data redundancy in an array with a minimum of three disks.Data is striped across all disks and a parity block (P) for each data block is written on the same stripe. If one physical disk fails, the data from the failed disk can be rebuilt onto a replacement disk. No data is lost in the case of a single disk failure, but if a second disk fails before data can be rebuilt to a replacement drive, all data in the array will be lost.In RAID 5+Spare, one disk in the array is left empty. If a drive in the array fails, the data from the failed disk is automatically rebuilt to the empty or “spare” disk.