On 01/07/2012 12:20, Jonathan Tripathy wrote:
Hi Everyone,
We have a few servers that use md raid with mdadm. Each server has 4
arrays (md0,md1,md2,md3). md0,1,2 are small and md3 is very large.
Every Sunday at 4:22am, the servers will start to resync. Here is some
text from /var/log/messages for one of the servers:
Jul 1 04:22:01 server1 kernel: md: syncing RAID array md0
Jul 1 04:22:01 server1 kernel: md: minimum _guaranteed_
reconstruction speed: 1000 KB/sec/disc.
Jul 1 04:22:01 server1 kernel: md: using maximum available idle IO
bandwidth (but not more than 200000 KB/sec) for reconstruction.
Jul 1 04:22:01 server1 kernel: md: using 128k window, over a total of
104320 blocks.
Jul 1 04:22:01 server1 kernel: md: delaying resync of md2 until md0
has finished resync (they share one or more physical units)
Jul 1 04:22:01 server1 kernel: md: delaying resync of md3 until md0
has finished resync (they share one or more physical units)
Jul 1 04:22:05 server1 kernel: md: md0: sync done.
Jul 1 04:22:05 server1 kernel: md: delaying resync of md3 until md2
has finished resync (they share one or more physical units)
Jul 1 04:22:05 server1 kernel: md: delaying resync of md2 until md3
has finished resync (they share one or more physical units)
Jul 1 04:22:05 server1 kernel: md: syncing RAID array md3
Jul 1 04:22:05 server1 kernel: md: minimum _guaranteed_
reconstruction speed: 1000 KB/sec/disc.
Jul 1 04:22:05 server1 kernel: md: using maximum available idle IO
bandwidth (but not more than 200000 KB/sec) for reconstruction.
Jul 1 04:22:05 server1 kernel: md: using 128k window, over a total of
1888295936 blocks.
/proc/mdstat shows a progress bar for the array that is currently
"re-syncing" (in the above case, md3). However, the disks in the
servers seem fine, and it always seems to happen in the early hours of
Sunday morning at 4:22am.
The issue gets further complicated as not all arrays are re-synced and
I can seem to find a pattern as to what's selected. All I know is that
at 4:22, mdadm will "come alive" and attempt to do re-syncing of some
(or all) of the arrays. On each of the servers, 3 of the arrays are
small and one is large; this leads to the phenomenon that when we wake
up on Sunday morning, a "random" selection of the servers will still
be syncing (as mdadm has decided to "pick" the large md3 array to
resync).
Here is output from /var/log/messages on a server that has only
decided to re-sync 2 small arrays (md0 and md2):
Jul 1 04:22:01 server3 kernel: md: syncing RAID array md0
Jul 1 04:22:01 server3 kernel: md: minimum _guaranteed_
reconstruction speed: 1000 KB/sec/disc.
Jul 1 04:22:01 server3 kernel: md: using maximum available idle IO
bandwidth (but not more than 200000 KB/sec) for reconstruction.
Jul 1 04:22:01 server3 kernel: md: using 128k window, over a total of
104320 blocks.
Jul 1 04:22:01 server3 kernel: md: delaying resync of md2 until md0
has finished resync (they share one or more physical units)
Jul 1 04:22:02 server3 kernel: md: md0: sync done.
Jul 1 04:22:02 server3 kernel: md: syncing RAID array md2
Jul 1 04:22:02 server3 kernel: md: minimum _guaranteed_
reconstruction speed: 1000 KB/sec/disc.
Jul 1 04:22:02 server3 kernel: md: using maximum available idle IO
bandwidth (but not more than 200000 KB/sec) for reconstruction.
Jul 1 04:22:02 server3 kernel: md: using 128k window, over a total of
1052160 blocks.
Jul 1 04:22:15 server3 kernel: md: md2: sync done
What's going on? Am I missing something here? Is data on the arrays at
risk? We're using CentOS 5 with mdadm v2.6.9. Kernel version is
2.6.18-274.18.1.el5
Any help is appreciated.
Upon further reading, I've discovered that these "resyncs" are due to
the cron raid-checks that occur. However, most of my questions still stand:
- Why aren't all arrays checked?
- Why are the checked arrays different each week? (Although md0 and md2
seem to be favorites!)
- Is data at risk during these check times? If not, why does mdstat
report them are "resyncing" and not simply "checking"?
- Is it safe to disable these checks? Would monitoring the SMART status
of the disks serve as a good substitute?
Any help in answering these questions is appreciated
Thanks
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