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On 08/09/2010 11:08 AM, Sebastian Hetze wrote:
<blockquote cite="mid:20100809090822.A65A23030011@mail.linux-ag.de"
type="cite">
<pre wrap="">Hi *,
What is your opinion and possibly your experience with using
no-disk-barrier and no-disk-flushes without BBU RAID? The reason for
me asking is the huge latency I suffer using flushes in my setup
where I run several virtual KVM instances in DRBD containers without
BBU RAID. These virtual systems frequently flush disks and these
operations occasionally queue up to a substantial epoch of 100 or even
higher.
</pre>
</blockquote>
Sebastian,<br>
<br>
See also my other 2 messages to the list, mailed yesterday and
today.<br>
After some testing on our new database cluster,<br>
I'm seeing a huge latency in writing small packets to disk with
flushes.<br>
Now I'm going to use protocol C, no-disk-barrier, no-disk-flushes,
and no BBU on primary and secondary.<br>
<br>
Your message helped me thinking about the risks.<br>
<br>
Both our servers have 2 power supplies, connected to 2 power feeds.<br>
So in case of a power failure of one feed, both servers will still
be running.<br>
<br>
Just like you mention, only in a complete power failure in the
datacentre,<br>
drbd will loose data, but at that moment all other servers using the
database server are also offline.<br>
<br>
On the database server we're using PostgreSQL.<br>
PostgreSQL is ACID-compliant, so the data on disk should not be
corrupt.<br>
It could be possible that we lost some database insert/updates,<br>
but that's a risk I'm willing to accept, looking at the small change
that all power is lost.<br>
<br>
Regards,<br>
Robert Verspuy<br>
<br>
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