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Old 04-20-2011, 10:56 AM   #1
rjo98
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Registered: Jun 2009
Location: US
Distribution: RHEL, CentOS
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Help understanding /prov/mdstat


I had a server that was hard powered down, now I notice when looking in /proc/mdstat, it shows the following. I'm guessing when my system went down hard, something got messed up, but I dont understand what exactly its doing by resyncing. All my data on md0 and md1 appears to be there. Both volumes are RAID5setup in the RAID BIOS upon boot. Does anyone know what its doing exactly? Since its a hardware RAID I'd think any array rebuilding would be done through that, although this says resync. I tried googling and reading the first page of results, but its no clearer to me really.

Personalities : [raid1]
read_ahead 1024 sectors
Event: 2
md0 : active raid1 sdb1[1] sda1[0]
859549696 blocks [2/2] [UU]
resync=DELAYED
md1 : active raid1 sdb2[1] sda2[0]
859533632 blocks [2/2] [UU]
[>....................] resync = 2.1% (18808576/859533632) finish=1404.8min speed=9971K/sec
unused devices: <none>

Also, what happens if people start adding data to the server before these resyncings finish? will that cause problems?
 
Old 04-20-2011, 11:59 AM   #2
lystor
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Registered: May 2010
Location: Ukraine, Donetsk
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Quote:
Originally Posted by rjo98 View Post
Both volumes are RAID5setup in the RAID BIOS upon boot. Does anyone know what its doing exactly? Since its a hardware RAID I'd think any array rebuilding would be done through that, although this says resync. I tried googling and reading the first page of results, but its no clearer to me really.

Personalities : [raid1]
read_ahead 1024 sectors
Event: 2
md0 : active raid1 sdb1[1] sda1[0]
859549696 blocks [2/2] [UU]
resync=DELAYED

md1 : active raid1 sdb2[1] sda2[0]
859533632 blocks [2/2] [UU]
[>....................] resync = 2.1% (18808576/859533632) finish=1404.8min speed=9971K/sec
unused devices: <none>
Hi
md0 is a software raid1 (mirror) of sda1 and sdb1
md1 is a software raid1 (mirror) of sda2 and sdb2.
These software raid's were created by mdadm tool.

RAID1 resync is a process of copying data from first to second or from second to first RAID HDD.

Quote:
Originally Posted by rjo98 View Post
Also, what happens if people start adding data to the server before these resyncings finish? will that cause problems?
No. Main problem - RAID read/write speed will be decreased.

Last edited by lystor; 04-20-2011 at 12:03 PM.
 
1 members found this post helpful.
Old 04-20-2011, 12:17 PM   #3
rjo98
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Distribution: RHEL, CentOS
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Thanks. I was totally confused because on that server i do have a /dev/md0 and a /dev/md1, so i thought it was talking about those! now it makes perfect sense, many thanks!
 
  


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