Обсуждение: postgresql cluster on SAN

On 9/09/2010 10:27 AM, Lazaro Ruben Garcia Martinez wrote:
> Hello everyone:
>
> I am a student of the University of Informatics Science in Cuba. I
> want create a postgresql cluster and I have two servers but I have a
> doubt. Is possible to create a cluster of postgresql server by sharing
> the database file on a SAN?

No, PostgreSQL does not support shared-storage clsutering. Use one of
the replication-based clustering options like Bucardo or Slony.

Added to FAQ after "What replication solutions are available?":

http://wiki.postgresql.org/wiki/FAQ#Is_possible_to_create_a_shared-storage_postgresql_server_cluster.3F

--
Craig Ringer

Tech-related writing at http://soapyfrogs.blogspot.com/

On Wed, Sep 8, 2010 at 9:02 PM, Lazaro Ruben Garcia Martinez
<lgarciam@estudiantes.uci.cu> wrote:
> Thank you very much for your answer, In the cluster that i said before I
> need only failover.
> In the documentation of postgresql I read about the Shared Disk Failover,
> this tecnique avoids synchronization overhead by having only one copy of the
> database. It uses a single disk array that is shared by multiple servers. If
> the main database server fails, the standby server is able to mount and
> start the database as though it was recovering from a database crash. This
> allows rapid failover with no data loss. One disadvantage is that the
> standby server should never access the shared storage while the primary
> server is running.
>
> For these resons is posible to use a SAN?

Yes, however, a SAN is not a replacement for some kind of streaming
replication in case you need to recover a database to a previous
uncorrupted state or should the SAN fail in some catastrophic way.
You need to look up "fencing" for your servers.


--
To understand recursion, one must first understand recursion.

  On 09/08/10 8:02 PM, Lazaro Ruben Garcia Martinez wrote:
> Thank you very much for your answer, In the cluster that i said before
> I need only failover.
> In the documentation of postgresql I read about the Shared Disk
> Failover, this tecnique avoids synchronization overhead by having only
> one copy of the database. It uses a single disk array that is shared
> by multiple servers. If the main database server fails, the standby
> server is able to mount and start the database as though it was
> recovering from a database crash. This allows rapid failover with no
> data loss. One disadvantage is that the standby server should never
> access the shared storage while the primary server is running.
>
> For these resons is posible to use a SAN?

sure.

you'll also want cluster management software to coordinate that, such as
Heartbeat, Veritas Cluster Service, etc.   most vendors who design
failover clusters use some sort of storage fencing, such that the
standby host *can't* access the shared storage until the 'fencing' is
switched.  this is often done via port disable on a managed switch (FC
or Ethernet).

On 9/09/2010 11:02 AM, Lazaro Ruben Garcia Martinez wrote:
> Thank you very much for your answer, In the cluster that i said before I need only failover.
> In the documentation of postgresql I read about the Shared Disk Failover, this tecnique avoids synchronization
overheadby having only one copy of the database. It uses a single disk array that is shared by multiple servers. If the
maindatabase server fails, the standby server is able to mount and start the database as though it was recovering from
adatabase crash. This allows rapid failover with no data loss. One disadvantage is that the standby server should never
accessthe shared storage while the primary server is running. 
> For these resons is posible to use a SAN?

Yes. See:

http://wiki.postgresql.org/wiki/Shared_Storage

Setting it up isn't trivial and if you mess it up, you *WILL* get
massive data corruption. If your shared storage dies, you still lose all
your data.

Personally, I favour replication.

Anyway, added a reference to [[Shared_Storage]] for failover-only
clustering to the faq entry posted earlier.


--
Craig Ringer

Tech-related writing at http://soapyfrogs.blogspot.com/