I assume that you're only running MySQL on one machine at a time, and
using drbd to keep a hot copy of the block device? Or are you running the
commercial MySQL cluster product?
The current setup is to use drbd to keep a hot copy of the block device.
I don't have enough RAM to hold the database in memory (the MySQL
cluster requires it all to be in RAM - no good for large db's)
This sounds well within the capabilities of your hardware. I certainly
don't expect DBMail to fall over and die. But, please do let us know if
you have to do any interesting tuning. A brief whitepaper would be grand!
Once I get it all up and running and in production I'll definitely write
to the list with how I set it up (I have to do this for our internal
documentation anyway)
If you're going all out, a battery backed user accessible cache like a
MicroMemory -- www.umem.com -- or the Gigabyte I-RAM --
http://www.gigabyte.com.tw/Products/Storage/Default.aspx -- (much
cheaper!) will allow you to place the filesystem's journal on that device.
This is a little different than battery backed RAID controllers, because
now the filesystem itself is in control.
That's a great looking device. I'll have to see if our 1U servers can
fit it :)
If I had postgres running on one server and mysql on the other, this
would be a perfect solution IMO. Just deciding on whether the added
complexity of running two db's is worth it.
How would you sync the data between the two databases? Surely not on the
block device anymore...
When I first installed my test systems I had MySQL in master-master
replication which worked great, but my bubble was burst with the IMAP ID
not being guaranteed to be incrementing for each message. I found that
the traffic on the network using the built-in replication was about 20%
of the traffic on the network using drbd (plus writes should be faster)
The reason to try drbd is that it looked fairly easy to fail over and
back, but now that I think of it a split-brain situation is going to
cause data loss no matter which way it's resolved. I'll have to do some
research on failing over MySQL and Postgres master-slave configurations.
Regards,
Josh.
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