3DM 2 Online Help

0021 Downgrade UDMA mode
Event Type
Warning
Cause
The 3ware RAID controller has downgraded the UDMA transfer rate between the controller and the ATA disk drives. This message only applies to parallel ATA and certain legacy serial ATA drives.
Background Information
The 3ware RAID controller communicates to the ATA disk drives through the Ultra DMA (UDMA) protocol. This protocol ensures data integrity across the ATA cable by appending a Cyclical Redundancy Check (CRC) for all ATA data that is transferred. If the data becomes corrupted between the drive and the 3ware RAID controller (because of an intermittent or poor quality cable connection) the 3ware RAID controller detects this as a UDMA CRC or cable error. The 3ware RAID controller then retries the failed command three times at the current UDMA transfer rate. If the error persists, it lowers the UDMA transfer rate (for example, from UDMA 100 to UDMA 66) and retries another three times.
Action
Check for possible causes of UDMA CRC errors such as defective or poor quality interface cables or cable routing problems through electrically noisy environments (for instance, cables are too close to the power supply). Also check for cables which are not standard or exceed the ATA specification. A list of cables for use with 3ware controllers is available at http://3ware.com/products/cables.asp.

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