34 lines
1.6 KiB
Text
34 lines
1.6 KiB
Text
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checkarray notes
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================
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checkarray will run parity checks across all your redundant arrays. By
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default, it is configured to run on the first Sunday of each month, at 01:06
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in the morning. This is realised by asking cron to wake up every Sunday with
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/etc/cron.d/mdadm, but then only running the script when the day of the month
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is less than or equal to 7. See #380425.
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Cron will try to run the check at "idle I/O priority" (see ionice(1)), so that
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the check does not overload the system too much. Note that this will only
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work if all the component devices of the array employ the (default) "cfq" I/O
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scheduler. See the kernel documentation[0] for information on how to verify
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and modify the scheduler. checkarray does not verify this for you.
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0. http://www.kernel.org/doc/Documentation/block/switching-sched.txt
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If you manually invoke checkarray, it runs with default I/O priority. Should
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you need to run a check at a higher (or lower) I/O priority, then have a look
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at the --idle, --slow, --fast, and --realtime options.
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'check' is a read-only operation, even though the kernel logs may suggest
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otherwise (e.g. /proc/mdstat and several kernel messages will mention
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"resync"). Please also see question 21 of the FAQ.
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If, however, while reading, a read error occurs, the check will trigger the
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normal response to read errors which is to generate the 'correct' data and try
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to write that out - so it is possible that a 'check' will trigger a write.
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However in the absence of read errors it is read-only.
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You can cancel a running array check with the -x option to checkarray.
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-- martin f. krafft <madduck@debian.org> Thu, 02 Sep 2010 10:27:29 +0200
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