Обсуждение: Postgres on NAS/NFS
I am considering running a Postgres with the database hosted on a NAS via NFS. I have read a few things on the Web sayingthis is not recommended, as it will be slow and could potentially cause data corruption. My goal is to have the database on a shared filesystem so in case of server failure, I can start up a standby Postgres serverand point it to the same database. I would rather not use a SAN as I have heard horror stories about managing them.Also they are extremely expensive. A DAS would be another option, but I'm not sure if a DAS can be connected to twoservers for server failover purposes. Currently I am considering not using a shared filesystem and instead using replication between the two servers. I am wondering what solutions have others used for my active-passive Postgres failover scenario? Is a NAS still not a recommendedapproach? Will a DAS work? Or is replication the best approach?
I think SAN is better for block access instead of file access (NAS) -----Mensaje original----- De: pgsql-admin-owner@postgresql.org [mailto:pgsql-admin-owner@postgresql.org] En nombre de Bryan Keller Enviado el: miércoles, 09 de febrero de 2011 05:00 p.m. Para: pgsql-admin@postgresql.org Asunto: [ADMIN] Postgres on NAS/NFS I am considering running a Postgres with the database hosted on a NAS via NFS. I have read a few things on the Web saying this is not recommended, as it will be slow and could potentially cause data corruption. My goal is to have the database on a shared filesystem so in case of server failure, I can start up a standby Postgres server and point it to the same database. I would rather not use a SAN as I have heard horror stories about managing them. Also they are extremely expensive. A DAS would be another option, but I'm not sure if a DAS can be connected to two servers for server failover purposes. Currently I am considering not using a shared filesystem and instead using replication between the two servers. I am wondering what solutions have others used for my active-passive Postgres failover scenario? Is a NAS still not a recommended approach? Will a DAS work? Or is replication the best approach? -- Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-admin
On Wed, Feb 9, 2011 at 2:59 PM, Bryan Keller <bryanck@gmail.com> wrote: > I am considering running a Postgres with the database hosted on a NAS via NFS. I have read a few things on the Web sayingthis is not recommended, as it will be slow and could potentially cause data corruption. > > My goal is to have the database on a shared filesystem so in case of server failure, I can start up a standby Postgresserver and point it to the same database. I would rather not use a SAN as I have heard horror stories about managingthem. Also they are extremely expensive. A DAS would be another option, but I'm not sure if a DAS can be connectedto two servers for server failover purposes. > > Currently I am considering not using a shared filesystem and instead using replication between the two servers. > > I am wondering what solutions have others used for my active-passive Postgres failover scenario? Is a NAS still not a recommendedapproach? Will a DAS work? Or is replication the best approach? DAS will absolutely work. Just be careful to fence things properly so that you don't end up with 2 servers trying to start the data directory at the same time. It will lead to some pretty nasty corruption. > > -- > Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-admin >
On 02/09/2011 03:49 PM, Jim Mlodgenski wrote: > On Wed, Feb 9, 2011 at 2:59 PM, Bryan Keller<bryanck@gmail.com> wrote: >> I am considering running a Postgres with the database hosted on a NAS via NFS. I have read a few things on the Web sayingthis is not recommended, as it will be slow and could potentially cause data corruption. >> >> My goal is to have the database on a shared filesystem so in case of server failure, I can start up a standby Postgresserver and point it to the same database. I would rather not use a SAN as I have heard horror stories about managingthem. Also they are extremely expensive. A DAS would be another option, but I'm not sure if a DAS can be connectedto two servers for server failover purposes. >> >> Currently I am considering not using a shared filesystem and instead using replication between the two servers. >> >> I am wondering what solutions have others used for my active-passive Postgres failover scenario? Is a NAS still not arecommended approach? Will a DAS work? Or is replication the best approach? > DAS will absolutely work. Just be careful to fence things properly so > that you don't end up with 2 servers trying to start the data > directory at the same time. It will lead to some pretty nasty > corruption. > >> -- >> Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org) >> To make changes to your subscription: >> http://www.postgresql.org/mailpref/pgsql-admin >> Jim is right, be very careful to fence things properly. Also, depending on how the NAS/DAS is mounted to the servers you may need to tweak permissions. I've seen NFS scenarios where the postgres user on the secondary machine has a different UID than the one on the source box and the result was a mount point owned by nobody:nobody which of course disallows postgres from accessing the file system. -- --------------------------------------------- Kevin Kempter - Constent State A PostgreSQL Professional Services Company www.consistentstate.com ---------------------------------------------
Hello, I have had the experience of running a database hosted on a dedicated NFS share. I have not had any problems. I would rather have this solution than having to use SAN, due to the flexibility I would get plus the less overhead in management. I recommend that you skim through a paper from Oracle/Netapp (from 2004, I think), where they talk a little bit about running a database on NFS (I'm not recommending neither Oracle, nor Netapp). But I think it's worth to mention it because it clarified a few things to me. In this scenario, the conclusion I get is that performance gain in a SAN does not payoff the management overhead you get. Specially in the scenario you're describing, which does not seem to have a heavy usage. Paying close attention to details to avoid any corruption issue in a shared environment, I don't think it would be a problem going for NFS. Regards, ~Frederiko Costa Linkedin profile: http://www.linkedin.com/in/frederikocosta On Wed, Feb 9, 2011 at 11:59 AM, Bryan Keller <bryanck@gmail.com> wrote: > I am considering running a Postgres with the database hosted on a NAS via NFS. I have read a few things on the Web sayingthis is not recommended, as it will be slow and could potentially cause data corruption. > > My goal is to have the database on a shared filesystem so in case of server failure, I can start up a standby Postgresserver and point it to the same database. I would rather not use a SAN as I have heard horror stories about managingthem. Also they are extremely expensive. A DAS would be another option, but I'm not sure if a DAS can be connectedto two servers for server failover purposes. > > Currently I am considering not using a shared filesystem and instead using replication between the two servers. > > I am wondering what solutions have others used for my active-passive Postgres failover scenario? Is a NAS still not a recommendedapproach? Will a DAS work? Or is replication the best approach? > > -- > Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-admin >
On 2/11/11 9:09 AM, Frederiko Costa wrote: > Paying close attention to details to avoid any corruption issue in a > shared environment, I don't think it would be a problem going for NFS. FYI -- beware of NFS related kernel bugs in recent Red Hat 5.x kernels: http://archives.postgresql.org/pgsql-hackers/2011-01/msg02611.php Joe -- Joe Conway credativ LLC: http://www.credativ.us Linux, PostgreSQL, and general Open Source Training, Service, Consulting, & 24x7 Support
On Thu, Feb 10, 2011 at 2:59 AM, Bryan Keller <bryanck@gmail.com> wrote: > I am considering running a Postgres with the database hosted on a NAS via NFS. I have read a few things on the Web sayingthis is not recommended, as it will be slow and could potentially cause data corruption. Its not recommended if you have a crap NFS implementation. I think it was about 10 years ago I ran Oracle under Solaris with a Netapp for storage. Rock solid, supported configuration, and actually outperformed using local disk. Hopefully the open source NFS clients have caught up by now - if you see problem reports or recommendations, pay attention to the platform and implementation rather than the protocol. -- Stuart Bishop <stuart@stuartbishop.net> http://www.stuartbishop.net/
Thanks for the feedback. It sounds like NFS is a viable solution nowadays. I a still going to shoot for using iSCSI, givenit is a block-level protocol rather than file-level, it seems to me it would be better suited to database I/O. On Feb 14, 2011, at 2:07 AM, Stuart Bishop wrote: > On Thu, Feb 10, 2011 at 2:59 AM, Bryan Keller <bryanck@gmail.com> wrote: > >> I am considering running a Postgres with the database hosted on a NAS via NFS. I have read a few things on the Web sayingthis is not recommended, as it will be slow and could potentially cause data corruption. > > Its not recommended if you have a crap NFS implementation. I think it > was about 10 years ago I ran Oracle under Solaris with a Netapp for > storage. Rock solid, supported configuration, and actually > outperformed using local disk. Hopefully the open source NFS clients > have caught up by now - if you see problem reports or recommendations, > pay attention to the platform and implementation rather than the > protocol. > > > -- > Stuart Bishop <stuart@stuartbishop.net> > http://www.stuartbishop.net/
On Mon, Feb 14, 2011 at 11:05 AM, Bryan Keller <bryanck@gmail.com> wrote: > Thanks for the feedback. It sounds like NFS is a viable solution nowadays. I a still going to shoot for using iSCSI, givenit is a block-level protocol rather than file-level, it seems to me it would be better suited to database I/O. Please note that until you've tested what happens when you pull the power plugs on the NAS server midday to simulate a motherboard / PS / UPS failure you don't really know how well this setup will survive when things go wrong. The worst time to find out your pgsql -> NAS setup can't handle sudden power loss etc is when the lights just went out.
Bryan Keller wrote:
> I am considering running a Postgres with the database hosted on a NAS
> via NFS. I have read a few things on the Web saying this is not
> recommended, as it will be slow and could potentially cause data
> corruption.
>
> My goal is to have the database on a shared filesystem so in case of
> server failure, I can start up a standby Postgres server and point it
> to the same database. I would rather not use a SAN as I have heard
> horror stories about managing them. Also they are extremely expensive.
> A DAS would be another option, but I'm not sure if a DAS can be
> connected to two servers for server failover purposes.
>
> Currently I am considering not using a shared filesystem and instead
> using replication between the two servers.
>
> I am wondering what solutions have others used for my active-passive
> Postgres failover scenario? Is a NAS still not a recommended approach?
> Will a DAS work? Or is replication the best approach?
The last section of this documentation page talks about NFS usage:
http://www.postgresql.org/docs/9.0/static/creating-cluster.html
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ It's impossible for everything to be true. +
Bryan Keller wrote: > It sounds like NFS is a viable solution nowadays. I a still going to shoot for using iSCSI, given it is a block-level protocolrather than file-level, it seems to me it would be better suited to database I/O. > Please digest carefully where Joe Conway pointed out that it took them major kernel-level work to get NFS working reliably on Linux. On anything but Solaris, I consider NFS a major risk still; nothing has improved "nowadays" relative to when people used to report regular database corruption running it on other operating systems. Make sure you read http://www.time-travellers.org/shane/papers/NFS_considered_harmful.html and mull over the warnings in there before you assume it will work, too. I don't think I've ever heard from someone happy with an iSCSI deployment, either. The only way you could make an NFS+iSCSI storage solution worse is to also use RAID5 on the NAS. I'd suggest taking a look at http://wiki.postgresql.org/wiki/Shared_Storage and consider how you're going to handle fencing issues as well here. One of the reasons SANs tend to be preferred in this area is because fencing at the fiber-channel switch level is pretty straightforward. DAS running over fiber-channel can offer the same basic features though, it's just not as common to use a switch in that environment. -- Greg Smith 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.us "PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books
On Wed, 2011-02-16 at 15:56 -0500, Greg Smith wrote: > Bryan Keller wrote: > > It sounds like NFS is a viable solution nowadays. I a still going to shoot for using iSCSI, given it is a block-levelprotocol rather than file-level, it seems to me it would be better suited to database I/O. > > > > Please digest carefully where Joe Conway pointed out that it took them > major kernel-level work to get NFS working reliably on Linux. On > anything but Solaris, I consider NFS a major risk still; nothing has > improved "nowadays" relative to when people used to report regular > database corruption running it on other operating systems. Make sure > you read > http://www.time-travellers.org/shane/papers/NFS_considered_harmful.html > and mull over the warnings in there before you assume it will work, too. > > I don't think I've ever heard from someone happy with an iSCSI > deployment, either. The only way you could make an NFS+iSCSI storage > solution worse is to also use RAID5 on the NAS. > > I'd suggest taking a look at > http://wiki.postgresql.org/wiki/Shared_Storage and consider how you're > going to handle fencing issues as well here. One of the reasons SANs > tend to be preferred in this area is because fencing at the > fiber-channel switch level is pretty straightforward. DAS running over > fiber-channel can offer the same basic features though, it's just not as > common to use a switch in that environment. In short, use DAS or a SAN. iSCSI suffers from all kinds of performance issues and NFS is just Michael Myers scary. With DAS systems able to handle up 192 drives over 6Gb/s a second these days, combined with a volume manager you can solve a lot of problems without breaking the bank. JD -- PostgreSQL.org Major Contributor Command Prompt, Inc: http://www.commandprompt.com/ - 509.416.6579 Consulting, Training, Support, Custom Development, Engineering http://twitter.com/cmdpromptinc | http://identi.ca/commandprompt