[DRBD-user] Identifying High iowait on DRBD Computers - SOLVED

Bart Coninckx bart.coninckx at telenet.be
Sat Feb 19 12:10:36 CET 2011

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


The speed of the resync depends on how you configured it. I seem to
remember you saying that the network was OK. This was actually why I
asked you in the beginning if you were using protocol C, since low I/O
on the primary node would be a result of a problem with write
performance on the second node, being it because of a problem with the
local storage there or with the DRBD link.

Anyways, good that you have it solved now. On to the next problem ;-)



On 02/19/11 01:10, Robinson, Eric wrote:
> Mystery appears to be solved!
> 
> The Ethernet card being used for DRBD replication was flaky in the old
> secondary. Apparently replication was sometimes going super slow. That
> explains why BOTH nodes had the high iowait problem when they were
> primary, but NEITHER had high iowait when they were secondary. We're
> using Protocol C, so processes on the primary kept queuing up waiting
> for io calls to complete because DRBD could not write them to the other
> node fast enough. 
> 
> It also explains my other question about the resync continually
> stalling. Seriously, did NOBODY in the list notice when I said the
> resync was going at a max of about 80K? When the NIC issue was resolved,
> resyncs now happen at 30,000K. :-)  
> 
> I discovered the problem when I rebooted the server again and it said
> "PCIe training error, slot3" and the system halted. You guessed it, slot
> 3 was the NIC doing the replication. I reseated the card and it came up
> fine and now replication is fast and I do not expect any more iowaits.
> Next task... Replace that NIC.
> 
> Thanks for everyone's help and suggestions.
> 
> --
> Eric Robinson
> 
> 
> 
> 
> 
> 
> 
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