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Data in ROSS starts as triple replicated on 3 different storage nodes, but then transforms to erasure coding giving resilience without major costs. ROSS currently uses 12/16 error coding, meaning that for every 12 blocks of data stored it actually writes 16 blocks. Up to four blocks could be damaged before ROSS is no longer able to recover data if a fifth block were damaged. In contrast, most RAID systems only have a 1 or 2 drive redundancy. ROSS scatters the 16 blocks across the storage nodes in a data center, improving the performance of data retrievals and further improving the resilience of the system (less chance that a node failure blocks access). Data can be accessed from any of the storage nodes. Currently the two systems (UAMS and UARK) are isolated from each other, not allowing replication. But the plans to join the two are in progress. Eventually all of the content in ROSS, regardless of which campus it physically lives on, would be accessible from either campus. Of course, if data living on one campus is accessed from the other campus, the access will be somewhat slower due to networking delays and bandwidth limitations going between campus.
As mentioned, soon Grace ROSS will have an option for replicating data in Fayetteville. However, even in this case I would not consider the copy in Fayetteville a true backup copy. Replication is good for maintaining data that needs high availability and equivalent performance regardless of which campus the data is accessed from. Replication also doubles the storage cost since it reduces available storage capacity at twice the rate that non-replicated storage does. We still recommended that researchers keep backup or archive copies of data somewhere else, even if replication is turned on.
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