An administrator is called to investigate slow write performance on a rack-mounted Windows Server 2022 file server that uses an internal RAID-5 array of six 12 Gb/s SAS disks.
Users report that large file copies stall for several seconds at a time, but the RAID manager still shows the virtual disk in an Optimal state and all drives healthy. However, the controller event log is filling with messages like:
SAS PHY 0: link CRC error count exceeded threshold
SAS link event: phy 0 critical error detected
No SMART media errors are reported on any drive, and no recent firmware or driver changes were made.
Which corrective action should the administrator perform first to address the root cause of the I/O slowdown?
Replace the RAID controller's cache-backup (BBU/Capacitor) module.
Start a full patrol read so the controller can re-map any bad blocks.
Reseat or replace the mini-SAS cable between the controller and backplane.
Update the firmware on every drive in the RAID set.
CRC or PHY errors on a SAS link indicate corrupted traffic between the controller and the drive backplane-not faulty media on the disks themselves. Vendor documentation notes that loose, damaged, or improperly routed SAS cables often manifest as link-speed drops, CRC counters, disks reported as briefly missing, or general sluggish I/O performance. Because the virtual disk remains Optimal and no SMART re-map or media errors are present, the most probable root cause is a signal-integrity problem on the physical path.
Reseating or replacing the mini-SAS cable is therefore the first (and least disruptive) step. If the cable is defective, CRC counters will stop climbing after it is corrected and performance should return to normal. Replacing batteries, updating firmware, or forcing patrol reads do not address the underlying communication errors and risk unnecessary downtime or additional load on a stressed array.