On 02/14/12 11:19, Victor Balada Diaz wrote:
We're having some troubles with AHCI under FreeBSD 8.2 and 8-STABLE. The error
is:
ahcich0: Timeout on slot 8
ahcich0: is 00000000 cs 00000100 ss 00000000 rs 00000100 tfd c0 serr 00000000
ahcich0: AHCI reset...
ahcich0: SATA connect time=0ms status=00000123
ahcich0: ready wait time=18ms
ahcich0: AHCI reset done: device found
(ada0:ahcich0:0:0:0): Request requeued
(ada0:ahcich0:0:0:0): Retrying command
(ada0:ahcich0:0:0:0): Command timed out
(ada0:ahcich0:0:0:0): Retrying command
ahcich0: Timeout on slot 8
ahcich0: is 00000000 cs 007ff000 ss 007fff00 rs 007fff00 tfd c0 serr 00000000
ahcich0: AHCI reset...
ahcich0: SATA connect time=0ms status=00000123
ahcich0: ready wait time=84ms
ahcich0: AHCI reset done: device found
(ada0:ahcich0:0:0:0): Request requeued
(ada0:ahcich0:0:0:0): Retrying command
(ada0:ahcich0:0:0:0): Command timed out
(ada0:ahcich0:0:0:0): Retrying command
(ada0:ahcich0:0:0:0): Request requeued
[...]
If we use old ATA driver we have no problems. If we just use the first disk
(ada0) with ahci,
no problems either. If we use both disks (ada0 and ada1) in gmirror setup with
ahci, we
got the above error. If we use both disks in gmirror with old ata driver, no
problems.
In both cases controller reports command status as 0xc0, that means
device is busy with the command. For NCQ commands it means that device
in in stage of processing command itself, not a head positioning or data
transfer. Enabling AHCI enables NCQ for the devices. That increases load
on both devices and the controller, and it is difficult to say who's
fault is here. SAMSUNG HD154UI disks AFAIR have 4k sectors that may have
big performance penalties when accessing small/misaligned data. I am not
sure how big that penalty can be in the worst case, especially since
disks by default cache writes, hiding the real load level. Relations
with gmirror is harder to explain. Depending on how you created it and
partitions it could cause more misaligned I/Os during rebuild. Using
gmirror also double concurrent load on the controller, but at this point
I have nothing to blame it for.
--
Alexander Motin
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