sbp, camcontrol, and Tagged Queuing
drew at mykitchentable.net
Tue Mar 29 10:59:37 PST 2005
On 3/17/2005 8:23 PM Bob Johnson wrote:
>On Thursday 17 March 2005 10:08 pm, Drew Tomlinson wrote:
>>I posted this a while back and am still having the same problem. Can
>>anyone offer any insight as to if the sbp man page suggestion about tagged
>>queuing is something I should try? Is there any risk of screwing up my
>>drives by trying this?
>Tagged queueing queues up multiple instructions for the drive simultaneously.
>The drive then attempts to sort them out and execute them in optimum order.
>Some drives that claim to support tagged queueing do not correctly do so, and
>don't perform well when it is used (and may lose data). If you set the queue
>size to one, as recommended in the passage you reference, then only one
>instruction will be issued to the drive at time, and it will behave like a
>drive without tagged queueing. It will do no harm to the drive. If the
>drive correctly implements tagged queueing, this will slow down the drive,
>but if it does not correctly implement it, then this may dramatically speed
>up the drive (and make it more stable). I have an external drive that
>manages 1.3 MBps transfers with queueing enabled, and 25 MBps transfers when
>I set the queue size to one.
>As for whether it will help your specific problem, I don't know, but I can't
>see how it would do any harm to test it.
Using the camcontrol utility, I found these drives were already set to "1"
blacklamb# camcontrol tags da2 -v
(pass3:sbp0:0:0:0): dev_openings 1
(pass3:sbp0:0:0:0): dev_active 0
(pass3:sbp0:0:0:0): devq_openings 1
(pass3:sbp0:0:0:0): devq_queued 0
(pass3:sbp0:0:0:0): held 0
(pass3:sbp0:0:0:0): mintags 2
(pass3:sbp0:0:0:0): maxtags 255
blacklamb# camcontrol tags da3 -v
(pass4:sbp0:0:0:1): dev_openings 1
(pass4:sbp0:0:0:1): dev_active 0
(pass4:sbp0:0:0:1): devq_openings 1
(pass4:sbp0:0:0:1): devq_queued 0
(pass4:sbp0:0:0:1): held 0
(pass4:sbp0:0:0:1): mintags 2
(pass4:sbp0:0:0:1): maxtags 255
Thus setting tagged queuing to "1" had no effect. Thanks again for your
explanation. I sure wish I could solve this issue!
>This issue is not specific to FreeBSD. Any OS that supports tagged queuing
>has problems with some drives.
>>da2 and da3 are two IDE drives in a firewire enclosure. These are also
>>the drives that come up "referenced" after restarting. What do these
>>errors mean? How can I correct them? Is the following section from the
>>sbp man page applicable to my situation?
>>Some (broken) HDDs don't work well with tagged queuing. If you have prob-
>>lems with such drives, try ``camcontrol [device id] tags -N 1'' to dis-
>>able tagged queuing.
>>Thanks for your help!
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