Обсуждение: NAS
Hello there!
A customer of our company would like to create a 2 nodes cluster connected to an external NAS storage. I would like to know if PostgreSQL supports its datafiles on this kind of storage and if this solution is certified.
Thanks
Marco Fortina
Senior Consultant
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BSC Consulting S.p.A.
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On Thu, Sep 17, 2009 at 8:06 AM, Marco Fortina <marco.fortina@bsc.it> wrote: > > Hello there! > > A customer of our company would like to create a 2 nodes cluster connected > to an external NAS storage. I would like to know if PostgreSQL supports its > datafiles on this kind of storage and if this solution is certified. If you're thinking a shared data directory, no, it won't work.
Marco Fortina wrote: > > Hello there! > > A customer of our company would like to create a 2 nodes cluster > connected to an external NAS storage. I would like to know if > PostgreSQL supports its datafiles on this kind of storage and if this > solution is certified. > active/standby type cluster, where only one server has the database software running at a time? in theory, should work. NAS storage is often NOT recommended for database table storage, however, as it often has funny quirks with regards to random access, concurrent access, and so forth. early versions of NFS were especially bad about this. most shared active/standby database high availability clusters use SAN block storage for this reason (fiberchannel, iscsi), and those often use 'fencing hardware' to be sure that the current standby system doesn't mount the file system when the other member is active. afaik, postgresql doesn't 'certify' anything, and certainly most of us on this email list do not speak for postgresql.org, we're mostly just users.
On Thu, Sep 17, 2009 at 5:53 PM, John R Pierce <pierce@hogranch.com> wrote: > afaik, postgresql doesn't 'certify' anything, and certainly most of us on > this email list do not speak for postgresql.org, we're mostly just users. However, many of us on the list ARE certifiable. But that's a different story.
On Thu, Sep 17, 2009 at 10:06 AM, Marco Fortina <marco.fortina@bsc.it> wrote: > > Hello there! > > A customer of our company would like to create a 2 nodes cluster connected > to an external NAS storage. I would like to know if PostgreSQL supports its > datafiles on this kind of storage and if this solution is certified. probably you are interested in the hot standby feature which is looking like a lock for 8.5. it's not exactly what you asked for (you need two complete copies of your database), but you get high availability, a queryable slave, and very strong data guarantees if combined with synchronous replication. As for NAS, just pretend it stands for: Nightmare (of) Administrator Scenario :-) merlin
On Thu, 17 Sep 2009, Marco Fortina wrote: > A customer of our company would like to create a 2 nodes cluster > connected to an external NAS storage. I would like to know if PostgreSQL > supports its datafiles on this kind of storage and if this solution is > certified. It's possible to setup this configuration with PostgreSQL, but all of the failover logic needs to be implemented with another program that does things like making sure only one copy of the database server can be active at a time. There are a couple of products that aim to handle this situation around. The FAQ for EnterpriseDB, who sells a commercial and supported version of PostgreSQL, talks about a couple of them in a helpful way: http://www.enterprisedb.com/products/allfaq.do I believe (and the FAQ suggests) they've got some setups like this among their customers already. Any of the projects they mention, Linux-HA, Red Hat Cluster, or Veritas Cluster, *could* be made to handle this goal, but it's going to require some customization to make that work for your customer. Should still be much less expensive when it's all said and done than similar offerings from the better known database vendors up-front, particularly when you consider the annual license fees of some of them for clustered solutions. Open-source projects such at PostgreSQL don't "certify" things as working; that's the sort of job better a company selling products. There are subtle hardware issues you need to be aware of with NAS to get both reliability and good performance, and as I already suggested lots of work to get the software right too. EnterpriseDB might have a certified production suggestion available, and you can find plenty of other companies who do this sort of work in the directory http://www.postgresql.org/support/professional_support ; I'd suggest you peruse that. Other companies on that list who I know do lots of custom replication consulting work include 2nd Quadrant, Command Prompt, and End Point. It would be pretty expensive to develop something in-house for this approach starting from scratch. I'd guess some number of months of full-time work for someone who was new to PostgreSQL and/or replication before they got it right. In my role as full-time pessimist, I would also suggest you definitely don't want to rely on anybody's first attempt at setting up replication, it's complicated and way to easy to screw it up in a way you won't notice until your data has already been eaten. -- * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD