On 2020-03-09 09:57:37 +0100, Laurenz Albe wrote: > On Sun, 2020-03-08 at 21:13 +0100, Peter J. Holzer wrote: > > But to be fair, a master/slave setup a la patroni isn't immune against > > "writing junk" either: Not on the hardware level (either of the nodes > > may have faulty hardware, and you may not notice it until too late), and > > more importantly, not on the software level. An erroneus DML statement > > (because of a bug in the application, or because the user/admin made a > > mistake) will cause the same wrong data to be distributed to all nodes > > (of course this also applies to RAC). > > Of course, nobody debates that. > > A high-availability solution only protects you from certain, well-defined > kinds of problems, usually related to hardware.
Right. And enterprise class SAN storage does this: It protects you from
failure of a single disk, a single cable, a single controller. Very
often you can physically spread out the components so that loss of a
whole rack (or server room) wouldn't affect availability. There are of
course limits: When a message sent over a single cable is corrupted in a
way that the checksum doesn't catch, corrupted data may be stored. But
then if data in RAM is corrupted that ECC doesn't catch, the same will
happen. A Patroni-based cluster isn't free of single points of failure
either.
So I don't buy the argument "X isn't a high availability solution
because it uses shared storage". While I have seen expensive SAN boxes
fail, I've also managed to wreck Patroni clusters. I'm not at all
convinced that the availability of a Patroni cluster is higher than that
of a failover cluster using shared storage.
hp
--
_ | Peter J. Holzer | Story must make more sense than reality.
|_|_) | |
| | | h...@hjp.at | -- Charles Stross, "Creative writing
__/ | http://www.hjp.at/ | challenge!"
signature.asc
Description: PGP signature
