Linux How To Disable SATA NCQ For Better Performance
This is the closest way to disabling it without using the "libata.force=noncq" kernel boot option is to set the queue to a depth of 1 which doesn't actually disable it.
Change the sdc below to match the device you want to disable NCQ for.
[root@officebox ~]# echo "1" > /sys/block/sdc/device/queue_depth
Errors that indicate you are having a performance issue are these in messages or dmesg relating to N........
status: { DRDY ERR } error: { ICRC ABRT } failed command: WRITE FPDMA QUEUED MCP55 Linux Errors
[ 2868.041375] ata1: EH in SWNCQ mode,QC:qc_active 0x40 sactive 0x40
[ 2868.041554] ata1: SWNCQ:qc_active 0x40 defer_bits 0x0 last_issue_tag 0x6
[ 2868.041556] dhfis 0x40 dmafis 0x40 sdbfis 0x20
[ 2868.041874] ata1: ATA_REG 0x41 ERR_REG 0x84
[ 2868.042013] ata1: tag : dhfis dmafis sdbfis sactive
[ 2868.042163] ata1: tag 0x6: 1 1 0 1
[ 2868.042301] ata1.00: exception Emask 0x1 SAct 0x40 SErr 0x400000 action 0x6 frozen
[........