[DRBD-user] MySQL-over-DRBD Performance

[Oliver Hookins]

>On Sat, Dec 15, 2007 at 12:28:44AM -0800, Art Age Software wrote:
>> I'm testing a configuration of MySQL 5 running on a 2-node DRBD
>> cluster. It is all configured and seems to be running fine. However,
>> upon  running the MySQL sql-bench tests I am seeing some surprising
>> (and alarming) results. I would be interested to hear from anybody who
>> has configured a similar setup to hear what sort of performance you
>> are seeing and what you have done to maximize performance of MySQL
>> over DRBD.
>> 
>> In my case, I am replacing a 3-year old pair of Dell 2850's (4GB,
>> Dual-Proc/Single-Core)  with a pair of new  Dell 2950's (8GB,
>> Dual-Proc/Quad-Core). Clearly, I expect to see an overall performance
>> boost from the new servers. And for most operations I am seeing better
>> performance. However for writes, I am seeing **worse** performance.
>> **But only when the database is located on the DRBD device.**

I've also set up a very similar cluster, and we have seen some performance
degration due to DRBD but I haven't numerically measured it, and it hasn't
impacted the cluster to the extent that we feel it warrants investigation.
That being said, we know that write performance isn't what we want it to be
but that has largely been attributed to running with 'sync_binlog' turned on
in MySQL. We are planning to mitigate this with a battery backed RAID card
so we can enable write-back caching without fear of data loss.

In some tests we've performed with write queries we've seen quite signifant
performance gains, in the hundreds of percent faster with the write-back
caching.

-- 
Regards,
Oliver Hookins
Anchor Systems