Edward Capriolo wrote: > On Fri, Jul 30, 2010 at 5:19 AM, Jeff Jansen <jeff.jansen@kkoncepts.net> wrote: >> Eugen Leitl <eugen@leitl.org> wrote on 2010-Jul-28: >>> Please do; I would be also quite interested as well. >> OK, my first pass at "HA Vserver with DRBD and Heartbeat" docs are up at: >> >> http://www.kkoncepts.net/HA >> >> Comments are enabled, so you can comment on the page if you've got suggestions, >> corrections, clarifications, etc. >> >> Jeff Jansen >> > >>> It does not scale as well as some other solutions, but it may have other advantages that you want (maybe better locking, maybe >>better fail over support...). > > A little off topic, but it is important distinction between scaling > and fail over. You really have to think hard on what your looking for. > > DRBD gives you disk replication Active/Passive and Active/Active 2 > nodes. Active Passive does not scale and active/active "scales" to two > nodes which really is not scaling, in best case if you scaled a web > server now you can handle twice the traffic, what happens when you get > three or ten times the traffic? That solution no longer holds up. I could be wrong, but I seem to remember that DRBD supports up to 3 nodes. > At this point you have to look into file systems that allow multiple > read/writes NFS or OCFS2. NFS does have locking but > it seems to be the general case that no one was any luck with it in > high contention situations. > http://cyrusimap.web.cmu.edu/imapd/faq.html. _ALL_ file systems that support concurrent access have performance problems in high contention situations. > OCFS2 is multi-attach file systems and it supports much stronger > locking semantics. Great! now that we have good locks and multi-mount > the question becomes what software is designed to work with this type > of file system? Can we have 10 nodes running mysql and > managing/working with the same MYD tables? It may work in theory but > practically I do not know of anyone doing it? You can do this with GFS/GFS2 or OCFS2. You have to set MySQL's locking to external. But the performance suffers as in any high-contention case. Performance of such a solution is in most cases going to be worse than a single node with a non-concurrent-access file system. > http://forums.mysql.com/read.php?144,205829,205829 That seems to be a weird isolated incident. There are plenty of accounts of it working fine. Possibly a bug in the particular version of MySQL that the poster was using. > The only software I know of that works well and scales on OCFS2 is > oracle, (probably because oracle corporation made both) Indeed, OCFS was initially designed for backing Oracle databases. > Most prominent scaling solutions cassandra, hbase, mongo, redis, hdfs. > Do NOT work with multi-attached file systems. That's due to performance reasons. For scaling you need performance to scale with the number of nodes you have. No shared-everything system will provide such performance due to the locking overheads. Most shared-everything solutions scale inversely. Gordan