During a scheduled maintenance window you discover that the status LED on drive 2 of a PowerEdge R740xd file server is solid amber and the PERC H740P controller reports the virtual disk as degraded. The four-disk RAID-10 volume is built from 600 GB 10 000 RPM SAS drives.
You hot-swap the failed drive with a brand-new 600 GB 10 000 RPM SAS drive of the same vendor and part number, but the controller refuses to start the rebuild and marks the replacement as "blocked" with the message physical disk size insufficient. Firmware on both the server and the drive are current, and all cabling is properly seated.
Which of the following is the MOST likely cause of the rebuild failure?
The rotational speed of the replacement drive does not exactly match the remaining drives, preventing the rebuild from starting.
The server must be completely powered off and on again before the controller can initialize the new drive for rebuild.
Write-back cache on the RAID controller was not flushed before removing the failed drive, so the controller has locked the rebuild.
The replacement drive's usable capacity is slightly smaller than the failed drive, so the controller will not add it to the array.
RAID controllers allocate space for an array based on the smallest member drive. Even drives that share the same advertised capacity often differ slightly in usable sectors because of manufacturing tolerances or differing firmware formats. If the replacement drive is even a few megabytes smaller than the original, the controller will not add it to the array and flags the disk as 'size insufficient'. A write-cache that was not flushed, a mismatch in spindle speed, or the lack of a power-cycle would not prevent a modern hardware controller from beginning a rebuild.
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What does a 'degraded' RAID state mean in a server?
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Why does a replacement drive with slightly less usable capacity cause a rebuild failure?
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What can an administrator do if the replacement drive is slightly smaller in usable capacity?