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

Robinson, Eric eric.robinson at psmnv.com
Sat Feb 19 01:10:50 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.

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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