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diff --git a/docs/Samba3-HOWTO/TOSHARG-HighAvailability.xml b/docs/Samba3-HOWTO/TOSHARG-HighAvailability.xml index 3d91f2c356..ce86dc1bc5 100644 --- a/docs/Samba3-HOWTO/TOSHARG-HighAvailability.xml +++ b/docs/Samba3-HOWTO/TOSHARG-HighAvailability.xml @@ -12,6 +12,9 @@ <title>Features and Benefits</title> <para> +<indexterm><primary>availability</primary></indexterm> +<indexterm><primary>intolerance</primary></indexterm> +<indexterm><primary>vital task</primary></indexterm> Network administrators are often concerned about the availability of file and print services. Network users are inclined toward intolerance of the services they depend on to perform vital task responsibilities. @@ -23,6 +26,10 @@ A sign in a computer room served to remind staff of their responsibilities. It r <blockquote> <para> +<indexterm><primary>fail</primary></indexterm> +<indexterm><primary>managed by humans</primary></indexterm> +<indexterm><primary>economically wise</primary></indexterm> +<indexterm><primary>anticipate failure</primary></indexterm> All humans fail, in both great and small ways we fail continually. Machines fail too. Computers are machines that are managed by humans, the fallout from failure can be spectacular. Your responsibility is to deal with failure, to anticipate it @@ -37,6 +44,9 @@ understand the problem. That is the purpose of this chapter. </para> <para> +<indexterm><primary>high availability</primary></indexterm> +<indexterm><primary>CIFS/SMB</primary></indexterm> +<indexterm><primary>state of knowledge</primary></indexterm> Parenthetically, in the following discussion there are seeds of information on how to provision a network infrastructure against failure. Our purpose here is not to provide a lengthy dissertation on the subject of high availability. Additionally, we have made @@ -53,6 +63,9 @@ applies to the deployment of Samba and other CIFS/SMB technologies. <title>Technical Discussion</title> <para> +<indexterm><primary>SambaXP conference</primary></indexterm> +<indexterm><primary>Germany</primary></indexterm> +<indexterm><primary>inspired structure</primary></indexterm> The following summary was part of a presentation by Jeremy Allison at the SambaXP 2003 conference that was held at Goettingen, Germany, in April 2003. Material has been added from other sources, but it was Jeremy who inspired the structure that follows. @@ -62,6 +75,9 @@ from other sources, but it was Jeremy who inspired the structure that follows. <title>The Ultimate Goal</title> <para> +<indexterm><primary>clustering technologies</primary></indexterm> +<indexterm><primary>affordable power</primary></indexterm> +<indexterm><primary>unstoppable services</primary></indexterm> All clustering technologies aim to achieve one or more of the following: </para> @@ -75,6 +91,10 @@ from other sources, but it was Jeremy who inspired the structure that follows. <para> A clustered file server ideally has the following properties: +<indexterm><primary>clustered file server</primary></indexterm> +<indexterm><primary>connect transparently</primary></indexterm> +<indexterm><primary>transparently reconnected</primary></indexterm> +<indexterm><primary>distributed file system</primary></indexterm> </para> <itemizedlist> @@ -98,9 +118,11 @@ from other sources, but it was Jeremy who inspired the structure that follows. <itemizedlist> <listitem> <para> +<indexterm><primary>state information</primary></indexterm> All TCP/IP connections are dependent on state information. </para> <para> +<indexterm><primary>TCP failover</primary></indexterm> The TCP connection involves a packet sequence number. This sequence number would need to be dynamically updated on all machines in the cluster to effect seamless TCP failover. @@ -108,6 +130,8 @@ from other sources, but it was Jeremy who inspired the structure that follows. </listitem> <listitem> <para> +<indexterm><primary>CIFS/SMB</primary></indexterm> +<indexterm><primary>TCP</primary></indexterm> CIFS/SMB (the Windows networking protocols) uses TCP connections. </para> <para> @@ -118,6 +142,7 @@ from other sources, but it was Jeremy who inspired the structure that follows. All current SMB clusters are failover solutions &smbmdash; they rely on the clients to reconnect. They provide server failover, but clients can lose information due to a server failure. +<indexterm><primary>server failure</primary></indexterm> </para></listitem> </itemizedlist> </para> @@ -126,6 +151,7 @@ from other sources, but it was Jeremy who inspired the structure that follows. <para> Servers keep state information about client connections. <itemizedlist> +<indexterm><primary>state</primary></indexterm> <listitem><para>CIFS/SMB involves a lot of state.</para></listitem> <listitem><para>Every file open must be compared with other open files to check share modes.</para></listitem> @@ -138,6 +164,13 @@ from other sources, but it was Jeremy who inspired the structure that follows. <title>The Front-End Challenge</title> <para> +<indexterm><primary>cluster servers</primary></indexterm> +<indexterm><primary>single server</primary></indexterm> +<indexterm><primary>TCP data streams</primary></indexterm> +<indexterm><primary>front-end virtual server</primary></indexterm> +<indexterm><primary>virtual server</primary></indexterm> +<indexterm><primary>de-multiplex</primary></indexterm> +<indexterm><primary>SMB</primary></indexterm> To make it possible for a cluster of file servers to appear as a single server that has one name and one IP address, the incoming TCP data streams from clients must be processed by the front-end virtual server. This server must de-multiplex the incoming packets at the SMB protocol @@ -145,6 +178,8 @@ from other sources, but it was Jeremy who inspired the structure that follows. </para> <para> +<indexterm><primary>IPC4 connections</primary></indexterm> +<indexterm><primary>RPC calls</primary></indexterm> One could split all IPC4 connections and RPC calls to one server to handle printing and user lookup requirements. RPC printing handles are shared between different IPC4 sessions &smbmdash; it is hard to split this across clustered servers! @@ -161,18 +196,27 @@ from other sources, but it was Jeremy who inspired the structure that follows. <title>Demultiplexing SMB Requests</title> <para> +<indexterm><primary>SMB requests</primary></indexterm> +<indexterm><primary>SMB state information</primary></indexterm> +<indexterm><primary>front-end virtual server</primary></indexterm> +<indexterm><primary>complicated problem</primary></indexterm> De-multiplexing of SMB requests requires knowledge of SMB state information, all of which must be held by the front-end <emphasis>virtual</emphasis> server. This is a perplexing and complicated problem to solve. </para> <para> +<indexterm><primary>vuid</primary></indexterm> +<indexterm><primary>tid</primary></indexterm> +<indexterm><primary>fid</primary></indexterm> Windows XP and later have changed semantics so state information (vuid, tid, fid) must match for a successful operation. This makes things simpler than before and is a positive step forward. </para> <para> +<indexterm><primary>SMB requests</primary></indexterm> +<indexterm><primary>Terminal Server</primary></indexterm> SMB requests are sent by vuid to their associated server. No code exists today to effect this solution. This problem is conceptually similar to the problem of correctly handling requests from multiple requests from Windows 2000 @@ -180,6 +224,7 @@ from other sources, but it was Jeremy who inspired the structure that follows. </para> <para> +<indexterm><primary>de-multiplexing</primary></indexterm> One possibility is to start by exposing the server pool to clients directly. This could eliminate the de-multiplexing step. </para> @@ -195,6 +240,12 @@ from other sources, but it was Jeremy who inspired the structure that follows. </para> <para> +<indexterm><primary>backend</primary></indexterm> +<indexterm><primary>SMB semantics</primary></indexterm> +<indexterm><primary>share modes</primary></indexterm> +<indexterm><primary>locking</primary></indexterm> +<indexterm><primary>oplock</primary></indexterm> +<indexterm><primary>distributed file systems</primary></indexterm> Many could be adopted to backend our cluster, so long as awareness of SMB semantics is kept in mind (share modes, locking, and oplock issues in particular). Common free distributed file systems include: @@ -212,6 +263,7 @@ from other sources, but it was Jeremy who inspired the structure that follows. </itemizedlist> <para> +<indexterm><primary>server pool</primary></indexterm> The server pool (cluster) can use any distributed file system backend if all SMB semantics are performed within this pool. </para> @@ -222,12 +274,18 @@ from other sources, but it was Jeremy who inspired the structure that follows. <title>Restrictive Constraints on Distributed File Systems</title> <para> +<indexterm><primary>SMB services</primary></indexterm> +<indexterm><primary>oplock handling</primary></indexterm> +<indexterm><primary>server pool</primary></indexterm> +<indexterm><primary>backend file system pool</primary></indexterm> Where a clustered server provides purely SMB services, oplock handling may be done within the server pool without imposing a need for this to be passed to the backend file system pool. </para> <para> +<indexterm><primary>NFS</primary></indexterm> +<indexterm><primary>interoperability</primary></indexterm> On the other hand, where the server pool also provides NFS or other file services, it will be essential that the implementation be oplock-aware so it can interoperate with SMB services. This is a significant challenge today. A failure @@ -245,12 +303,19 @@ from other sources, but it was Jeremy who inspired the structure that follows. <title>Server Pool Communications</title> <para> +<indexterm><primary>POSIX semantics</primary></indexterm> +<indexterm><primary>SMB</primary></indexterm> +<indexterm><primary>POSIX locks</primary></indexterm> +<indexterm><primary>SMB locks</primary></indexterm> Most backend file systems support POSIX file semantics. This makes it difficult to push SMB semantics back into the file system. POSIX locks have different properties and semantics from SMB locks. </para> <para> +<indexterm><primary>smbd</primary></indexterm> +<indexterm><primary>tdb</primary></indexterm> +<indexterm><primary>Clustered smbds</primary></indexterm> All <command>smbd</command> processes in the server pool must of necessity communicate very quickly. For this, the current <parameter>tdb</parameter> file structure that Samba uses is not suitable for use across a network. Clustered <command>smbd</command>s must use something else. @@ -267,6 +332,8 @@ from other sources, but it was Jeremy who inspired the structure that follows. </para> <itemizedlist> +<indexterm><primary>Myrinet</primary></indexterm> +<indexterm><primary>scalable coherent interface</primary><see>SCI</see></indexterm> <listitem><para> Proprietary shared memory bus (example: Myrinet or SCI [scalable coherent interface]). These are high-cost items. @@ -307,6 +374,8 @@ from other sources, but it was Jeremy who inspired the structure that follows. </para></listitem> <listitem><para> +<indexterm><primary>failure semantics</primary></indexterm> +<indexterm><primary>oplock messages</primary></indexterm> Failure semantics need to be defined. Samba behaves the same way as Windows. When oplock messages fail, a file open request is allowed, but this is potentially dangerous in a clustered environment. So how should interserver @@ -327,11 +396,16 @@ from other sources, but it was Jeremy who inspired the structure that follows. <title>A Simple Solution</title> <para> +<indexterm><primary>failover servers</primary></indexterm> +<indexterm><primary>exported file system</primary></indexterm> +<indexterm><primary>distributed locking protocol</primary></indexterm> Allowing failover servers to handle different functions within the exported file system removes the problem of requiring a distributed locking protocol. </para> <para> +<indexterm><primary>high-speed server interconnect</primary></indexterm> +<indexterm><primary>complex file name space</primary></indexterm> If only one server is active in a pair, the need for high-speed server interconnect is avoided. This allows the use of existing high-availability solutions, instead of inventing a new one. This simpler solution comes at a price &smbmdash; the cost of which is the need to manage a more @@ -340,6 +414,7 @@ from other sources, but it was Jeremy who inspired the structure that follows. </para> <para> +<indexterm><primary>virtual server</primary></indexterm> The <emphasis>virtual server</emphasis> is still needed to redirect requests to backend servers. Backend file space integrity is the responsibility of the administrator. </para> @@ -350,6 +425,11 @@ from other sources, but it was Jeremy who inspired the structure that follows. <title>High-Availability Server Products</title> <para> +<indexterm><primary>resource failover</primary></indexterm> +<indexterm><primary>high-availability services</primary></indexterm> +<indexterm><primary>dedicated heartbeat</primary></indexterm> +<indexterm><primary>LAN</primary></indexterm> +<indexterm><primary>failover process</primary></indexterm> Failover servers must communicate in order to handle resource failover. This is essential for high-availability services. The use of a dedicated heartbeat is a common technique to introduce some intelligence into the failover process. This is often done over a dedicated @@ -358,6 +438,10 @@ from other sources, but it was Jeremy who inspired the structure that follows. <para> <indexterm><primary>SCSI</primary></indexterm> +<indexterm><primary>Red Hat Cluster Manager</primary></indexterm> +<indexterm><primary>Microsoft Wolfpack</primary></indexterm> +<indexterm><primary>Fiber Channel</primary></indexterm> +<indexterm><primary>failover communication</primary></indexterm> Many failover solutions (like Red Hat Cluster Manager and Microsoft Wolfpack) can use a shared SCSI of Fiber Channel disk storage array for failover communication. Information regarding Red Hat high availability solutions for Samba may be obtained from @@ -365,12 +449,15 @@ from other sources, but it was Jeremy who inspired the structure that follows. </para> <para> +<indexterm><primary>Linux High Availability project</primary></indexterm> The Linux High Availability project is a resource worthy of consultation if your desire is to build a highly available Samba file server solution. Please consult the home page at <ulink url="http://www.linux-ha.org/">www.linux-ha.org/</ulink>. </para> <para> +<indexterm><primary>backend failures</primary></indexterm> +<indexterm><primary>continuity of service</primary></indexterm> Front-end server complexity remains a challenge for high availability because it must deal gracefully with backend failures, while at the same time providing continuity of service to all network clients. |