How do I use NCQ of Intel X25-E(SSD) on ahci(4)?

Ivan Voras ivoras at
Mon Dec 14 11:45:48 UTC 2009

2009/12/14 Alexander Motin <mav at>:
> Ivan Voras wrote:
>> 2009/11/18 Alexander Motin <mav at>:
>>> Ivan Voras wrote:
>>>> I know next to nothing about AHCI and drivers so this might be obviously
>>>> wrong but wouldn't a quick (i.e. MFC-able) obvious temporary fix be to say
>>>> numslots = min(get_minimum_tags_of_all_drives(), ...)
>>>> ?
>>> Problem is that SIM driver has no idea about devices capabilities, and
>>> also doesn't have method to resize queue after attach. In SCSI case,
>>> tags are random and only simultaneous number of request is limited, and
>>> this is handled fine by CAM. SATA NCQ is more restrictive, allowing to
>>> use only tags 0..(N-1). I am planning to make XPT inform SIM about
>>> supported tags for each device, to allow SIM to use that information
>>> while scheduling requests. I didn't do it yet, just because most of
>>> devices able to handle all 32 tags possible on SATA. This Intel SSD is
>>> one of rare exceptions.
>> Ok, (still thinking about something that could be MFC-able in an
>> emergency), how about adding a loader tunable integer instead of "32"?
> Just for note, it is already fixed and merged.

Thank you!

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