Shared file system
A user on Informix 11.70 / HP-UX asked how to set up the "shared file system" required for an SDS secondary: must the secondary see the primary's HP-UX logical volumes, and does it need its own dbspaces? Answers: no separate dbspaces; the SDS node needs writeable access to the same storage, though only one node should actually write at a time (I/O fencing recommended) — true even for updatable SDS, since DML is forwarded to the primary. Madison Pruet noted SDS nodes also coordinate via an SDS_ALTERNATE blobspace blob, so fencing can interfere with that communication. No concrete HP-UX/Serviceguard setup procedure was given, and the poster's final questions went unanswered.
Auto-generated by DrWatson from the posts below — may be imperfect; read the full thread.
Informix 11.7FC8 HP UX 31.1 I am setting up an SDS server but need some guidance: The Informix manuals specifies a "shared file system" for setting up an SDS server. My understanding is that I don't have to create any db spaces on the secondary server. Does this mean that the secondary should be able to see the lvs(HP UX) on the primary. How do I set up the shared file systems ?
Correct. The SDS needs writeable access to the same storage as the primary. Art On Aug 21, 2015 7:22 AM, "FLIP VAN WYNGAARDT" <flipv@raf.co.za> wrote: > Informix 11.7FC8 > HP UX 31.1 > > I am setting up an SDS server but need some guidance: > > The Informix manuals specifies a "shared file system" for setting up an SDS > server. My understanding is that I don't have to create any db spaces on > the > secondary server. Does this mean that the secondary should be able to see > the > lvs(HP UX) on the primary. How do I set up the shared file systems ? > > > > ******************************************************************************* > Forum Note: Use "Reply" to post a response in the discussion forum. > > --001a113fe66c7b9d0a051dd19de3
In order to avoid serious issues, the write access should be in one side only at a specific time. The SDS needs write access only when it's promoted to primary server. Exception is for the special spaces configured in the $ONCONFIG. Failure to get this "write only on one side at a time" may cause serious issues if both servers think they're primary. The situations that could lead to this include human error and some design issues that have been solved over time. In order to guarantee this, look for "I/O fencing" in your sharing technology.... it can be achieved in different ways, but it's important to have it. Regards. On Fri, Aug 21, 2015 at 1:43 PM, Art Kagel <art.kagel@gmail.com> wrote: > Correct. The SDS needs writeable access to the same storage as the primary. > > Art > On Aug 21, 2015 7:22 AM, "FLIP VAN WYNGAARDT" <flipv@raf.co.za> wrote: > > > Informix 11.7FC8 > > HP UX 31.1 > > > > I am setting up an SDS server but need some guidance: > > > > The Informix manuals specifies a "shared file system" for setting up an > SDS > > server. My understanding is that I don't have to create any db spaces on > > the > > secondary server. Does this mean that the secondary should be able to see > > the > > lvs(HP UX) on the primary. How do I set up the shared file systems ? > > > > > > > > > > ******************************************************************************* > > Forum Note: Use "Reply" to post a response in the discussion forum. > > > > > > --001a113fe66c7b9d0a051dd19de3 > > > > ******************************************************************************* > Forum Note: Use "Reply" to post a response in the discussion forum. > > -- Fernando Nunes Portugal http://informix-technology.blogspot.com My email works... but I don't check it frequently... --001a11c31f6ee3c827051dd1ee04
Does it still applies when I set up an updateable SDS server ?
Yes. The SDS secondary does not actually process the insert/update/delete statements, it passes them to the primary for processing and the primary informs the SDS what buffer pages need to be invalidated/reloaded from disk once the data has been modified. Art Art S. Kagel, President and Principal Consultant ASK Database Management www.askdbmgt.com Blog: http://informix-myview.blogspot.com/ Disclaimer: Please keep in mind that my own opinions are my own opinions and do not reflect on the IIUG, nor any other organization with which I am associated either explicitly, implicitly, or by inference. Neither do those opinions reflect those of other individuals affiliated with any entity with which I am affiliated nor those of the entities themselves. On Fri, Aug 21, 2015 at 8:39 AM, FLIP VAN WYNGAARDT <flipv@raf.co.za> wrote: > Does it still applies when I set up an updateable SDS server ? > > > > ******************************************************************************* > Forum Note: Use "Reply" to post a response in the discussion forum. > > --001a113fe66c51ad50051dd2a5c8
Will I have to use something like HP Serviceguard to share and "fence in" the lvs. How will it work when the secondary takes over as primary in a fail over situation ?
Does anyone have a procedure or instructions on how to share and "fence in" disks on HP-UX level in order to set up an SDS and primary servers.
Don't forget that the SDS servers and the primary server communicate via a blob space blob as well as the TCP network. This includes not only the LSN that the SDS nodes should process up to, but also the ability to shut down the primary even if the network is lost. Each shared disk server is constantly updating their blob and reading the current primary's blob to post their status and to know the status of the primary. The primary reads the blobs of each of the secondaries so it knows their status as well. Adding I/O fencing is adding a level of insurance, but it also means that you lose the ability to communicate amongst the nodes if there is a network issue. From: "Fernando Nunes" <domusonline@gmail.com> To: ids@iiug.org Date: 08/21/2015 08:07 AM Subject: Re: Shared file system [35623] Sent by: ids-bounces@iiug.org In order to avoid serious issues, the write access should be in one side only at a specific time. The SDS needs write access only when it's promoted to primary server. Exception is for the special spaces configured in the $ONCONFIG. Failure to get this "write only on one side at a time" may cause serious issues if both servers think they're primary. The situations that could lead to this include human error and some design issues that have been solved over time. In order to guarantee this, look for "I/O fencing" in your sharing technology.... it can be achieved in different ways, but it's important to have it. Regards. On Fri, Aug 21, 2015 at 1:43 PM, Art Kagel <art.kagel@gmail.com> wrote: > Correct. The SDS needs writeable access to the same storage as the primary. > > Art > On Aug 21, 2015 7:22 AM, "FLIP VAN WYNGAARDT" <flipv@raf.co.za> wrote: > > > Informix 11.7FC8 > > HP UX 31.1 > > > > I am setting up an SDS server but need some guidance: > > > > The Informix manuals specifies a "shared file system" for setting up an > SDS > > server. My understanding is that I don't have to create any db spaces on > > the > > secondary server. Does this mean that the secondary should be able to see > > the > > lvs(HP UX) on the primary. How do I set up the shared file systems ? > > > > > > > > > > ***************************************************************************= **** > > Forum Note: Use "Reply" to post a response in the discussion forum. > > > > > > --001a113fe66c7b9d0a051dd19de3 > > > > ***************************************************************************= **** > Forum Note: Use "Reply" to post a response in the discussion forum. > > -- Fernando Nunes Portugal http://informix-technology.blogspot.com My email works... but I don't check it frequently... --001a11c31f6ee3c827051dd1ee04 ***************************************************************************= **** Forum Note: Use "Reply" to post a response in the discussion forum.
I am a bit confused now about should I fence in the shared disks or not? We want to implement the communication manger to handle automatic fail over and load balancing.
Very valid point as we would expect coming from you. I'd say we're lacking some more documentation around this... At first I though you were considering SDS_LOGCHECK, but I understand you're referring to SDS_ALTERNATE. I may be missing something but I think this is only explained in the Administrator Reference.... If that's true I'd say it's insufficient, but it's probably too late to complain to you :) Regards On Mon, Aug 24, 2015 at 2:12 PM, Madison Pruet <mpruet@us.ibm.com> wrote: > Don't forget that the SDS servers and the primary server communicate via a > blob space blob as well as the TCP network. This includes not only the LSN > that the SDS nodes should process up to, but also the ability to shut down > the primary even if the network is lost. Each shared disk server is > constantly updating their blob and reading the current primary's blob to > post their status and to know the status of the primary. The primary reads > the blobs of each of the secondaries so it knows their status as well. > Adding I/O fencing is adding a level of insurance, but it also means that > you lose the ability to communicate amongst the nodes if there is a network > issue. > > From: "Fernando Nunes" <domusonline@gmail.com> > To: ids@iiug.org > Date: 08/21/2015 08:07 AM > Subject: Re: Shared file system [35623] > Sent by: ids-bounces@iiug.org > > In order to avoid serious issues, the write access should be in one side > only at a specific time. > The SDS needs write access only when it's promoted to primary server. > Exception is for the special spaces configured in the $ONCONFIG. > Failure to get this "write only on one side at a time" may cause serious > issues if both servers think they're primary. The situations that could > lead to this include human error and some design issues that have been > solved over time. > > In order to guarantee this, look for "I/O fencing" in your sharing > technology.... it can be achieved in different ways, but it's important to > have it. > > Regards. > > On Fri, Aug 21, 2015 at 1:43 PM, Art Kagel <art.kagel@gmail.com> wrote: > > > Correct. The SDS needs writeable access to the same storage as the > primary. > > > > Art > > On Aug 21, 2015 7:22 AM, "FLIP VAN WYNGAARDT" <flipv@raf.co.za> wrote: > > > > > Informix 11.7FC8 > > > HP UX 31.1 > > > > > > I am setting up an SDS server but need some guidance: > > > > > > The Informix manuals specifies a "shared file system" for setting up an > > > SDS > > > server. My understanding is that I don't have to create any db spaces > on > > > the > > > secondary server. Does this mean that the secondary should be able to > see > > > the > > > lvs(HP UX) on the primary. How do I set up the shared file systems ? > > > > > > > > > > > > > > > > > > ***************************************************************************= > **** > > > > Forum Note: Use "Reply" to post a response in the discussion forum. > > > > > > > > > > --001a113fe66c7b9d0a051dd19de3 > > > > > > > > > > ***************************************************************************= > **** > > > Forum Note: Use "Reply" to post a response in the discussion forum. > > > > > > -- > Fernando Nunes > Portugal > > http://informix-technology.blogspot.com > My email works... but I don't check it frequently... > > --001a11c31f6ee3c827051dd1ee04 > > > ***************************************************************************= > **** > > Forum Note: Use "Reply" to post a response in the discussion forum. > > > > ******************************************************************************* > Forum Note: Use "Reply" to post a response in the discussion forum. > > -- Fernando Nunes Portugal http://informix-technology.blogspot.com My email works... but I don't check it frequently... --001a113ff69c1b7a00051e3d9847