taskqueue timeout

[Matthew Dillon]

:Went from 10->15, and it took quite a bit longer into the backup before 
:the problem cropped back up.

    Try 30 or longer.  See if you can make the problem go away entirely.
    then fall back to 5 and see if the problem resumes at its earlier
    pace.

    --

    It could be temperature related.  The drives are being exercised
    a lot, they could very well be overheating.  To find out add more
    airflow (a big house fan would do the trick).

    --

    It could be that errors are accumulating on the drives, but it seems
    unlikely that four drives would exhibit the same problem.

    --

    Also make sure the power supply can handle four drives.  Most power
    supplies that come with consumer boxes can't under full load if you
    also have a mid or high-end graphics card installed.  Power supplies
    that come with OEM slap-together enclosures are not usually much better.

    Specifically, look at the +5V and +12V amperage maximums on the power
    supply, then check the disk labels to see what they draw, then
    multiply by 2.  e.g. if your power supply can do 30A at 12V and you have
    four drives each taking 2A at 12V (and typically ~half that at 5V), thats
    4x2x2 = 16A at 12V and you would probably be ok.

    To test, remove two of the four drives, reformat the ZFS to use just 2,
    and see if the problem reoccurs with just two drives.

						-Matt