hesela.devCommand-based switching (SATA)
Command-based switching restricts outstanding commands behind a SATA port multiplier to one downstream device at a time.
The host completes work for the selected device before issuing commands to another target. This restriction concerns the target, not a universal one-command queue. [1]
AHCI explicitly permits NCQ operation in this mode, with the active queue drained before changing targets. [2]
A busy target can delay access to other attached drives even while those drives could perform work independently. [3]
Relations
Citations
- SATA-IO Serial ATA Revision 2.6, section 16.7, page 545: command-based and FIS-based switching
- Intel AHCI 1.3.1, sections 3.1.1, 3.3.7, 3.3.16 and 9: capabilities and port-multiplier operation
- Scott Knowlton, Synopsys: Understanding SATA FIS-Based Switching (2013), connectivity and shared bandwidth
Sources & caveats
- SATA-IO sections were checked through indexed primary-specification text; direct PDF retrieval was unavailable. [1]