ISC2 Certified Secure Software Lifecycle Professional (CSSLP) Practice Question
Your SaaS company stores petabytes of customer backups in a distributed object-storage cluster that spans three cloud availability zones. Management requires eleven-nines (99.999999999 %) durability but wants lower capacity overhead than traditional three-way replication. Which storage configuration best satisfies these requirements?
Apply Reed-Solomon 10 + 4 erasure coding, distributing ten data shards and four parity shards across the three availability zones.
Configure RAID 0 striping across disks within a single zone to maximize throughput for backup storage.
Compress each backup with a lossless algorithm and store the single compressed file in an encrypted volume in one zone.
Keep three complete replicas of every object, with one full copy stored in each availability zone using synchronous replication.
Erasure coding improves durability by slicing each object into data and parity shards that are distributed across multiple fault domains; only a subset of the shards is needed to reconstitute the data. A Reed-Solomon 10 + 4 scheme stores ten data shards and four parity shards, tolerating the loss of up to four shards while adding only 40 % storage overhead-far less than the 200 % overhead of 3× replication-yet still achieving eleven-nines durability when spread across independent availability zones. Plain triple replication meets the durability target but wastes far more space, while RAID 0 and simple compression offer no fault tolerance, so they cannot ensure durability.
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What is erasure coding and how does it work?
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What is Reed-Solomon erasure coding?
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ISC2 Certified Secure Software Lifecycle Professional (CSSLP)