After successfully expanding an existing 4-disk RAID 5 array on a Linux file server to five disks, a systems administrator observes higher latency during write operations. The array is managed by the server's hardware controller. What is the most probable cause of the observed increase in write latency?
The overhead of parity calculations is higher now with the additional disk, increasing latency for write operations.
Suboptimal cable quality is causing a bottleneck in data transfer between the controller and the disks.
The disk recently added to the server is defective, causing a delay in the array's ability to write data effectively.
The block size of the array is not properly configured for the number of disks, leading to inefficient write operations.
RAID 5 utilizes distributed parity for data redundancy, which incurs a 'write penalty'. For small write operations, the controller must perform a read-modify-write cycle: read the old data, read the old parity, calculate the new parity, and then write the new data and new parity. This sequence of four I/O operations for a single logical write inherently adds latency. While adding a disk increases the number of spindles for parallel I/O, the fundamental overhead of managing parity across a wider stripe remains and can manifest as increased latency. Other issues like faulty hardware or block size misconfiguration are possible, but they are less likely to appear as a consistent latency increase immediately following a successful array expansion.
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