-## <a name="Demand-Attach File-Server (DAFS)"></a> Demand-Attach File-Server (DAFS)
+[[!toc levels=3]]
+
+# Demand-Attach File-Server (DAFS)
+
OpenAFS 1.5 contains Demand-Attach File-Server (DAFS). DAFS is a significant departure from the more _traditional_ AFS file-server and this document details those changes.
-<div>
- <ul>
- <li><a href="#Demand-Attach File-Server (DAFS)"> Demand-Attach File-Server (DAFS)</a></li>
- <li><a href="#Why Demand-Attach File-Server (D"> Why Demand-Attach File-Server (DAFS) ?</a></li>
- <li><a href="#An Overview of Demand-Attach Fil"> An Overview of Demand-Attach File-Server</a></li>
- <li><a href="#The Gory Details of the Demand-A"> The Gory Details of the Demand-Attach File-Server</a><ul>
- <li><a href="#Bos Configuration"> Bos Configuration</a></li>
- <li><a href="#File-server Start-up / Shutdown"> File-server Start-up / Shutdown Sequence</a></li>
- <li><a href="#Volume Finite-State Automata"> Volume Finite-State Automata</a></li>
- <li><a href="#Volume Least Recently Used (VLRU"> Volume Least Recently Used (VLRU) Queues</a></li>
- <li><a href="#Vnode Finite-State Automata"> Vnode Finite-State Automata</a></li>
- <li><a href="#Demand Salvaging"> Demand Salvaging</a></li>
- <li><a href="#File-Server Host / Callback Stat"> File-Server Host / Callback State</a></li>
- </ul>
- </li>
- <li><a href="#File-Server Arguments (relating"> File-Server Arguments (relating to Demand-Attach)</a></li>
- <li><a href="#Tools for Debugging Demand-Attac"> Tools for Debugging Demand-Attach File-Server</a><ul>
- <li><a href="#==fssync-debug=="> fssync-debug</a></li>
- <li><a href="#==salvsync-debug=="> salvsync-debug</a></li>
- <li><a href="#==state_analyzer=="> state_analyzer</a><ul>
- <li><a href="#Header Information"> Header Information</a></li>
- <li><a href="#Host Information"> Host Information</a></li>
- <li><a href="#Callback Information"> Callback Information</a></li>
- </ul>
- </li>
- </ul>
- </li>
- </ul>
-</div>
-
-## <a name="Why Demand-Attach File-Server (D"></a> Why Demand-Attach File-Server (DAFS) ?
+## Why Demand-Attach File-Server (DAFS) ?
On a traditional file-server, volumes are attached at start-up and detached only at shutdown. Any attached volume can be modified and changes are periodically flushed to disk or on shutdown. When a file-server isn't shutdown cleanly, the integrity of every attached volume has to be verified by the salvager, whether the volume had been modified or not. As file-servers grow larger (and the number of volumes increase), the length of time required to salvage and attach volumes increases, e.g. it takes around two hours for a file-server housing 512GB data to salvage and attach volumes !
Large portions of this document were taken / influenced by the presentation entitled [Demand Attach / Fast-Restart Fileserver](http://workshop.openafs.org/afsbpw06/talks/tkeiser-dafs.pdf) given by Tom Keiser at the [AFS and Kerberos Best Practices Workshop](http://workshop.openafs.org/) in [2006](http://workshop.openafs.org/afsbpw06/).
-## <a name="An Overview of Demand-Attach Fil"></a> An Overview of Demand-Attach File-Server
+## An Overview of Demand-Attach File-Server
Demand-attach necessitated a significant re-design of certain aspects of the AFS code, including:
- callbacks are no longer broken on shutdown
- instead, host / callback state is preserved across restarts
-## <a name="The Gory Details of the Demand-A"></a> The Gory Details of the Demand-Attach File-Server
+## The Gory Details of the Demand-Attach File-Server
-### <a name="Bos Configuration"></a> Bos Configuration
+### Bos Configuration
A traditional file-server uses the `bnode` type `fs` and has a definition similar to
bnode fs fs 1
- parm /usr/afs/bin/fileserver -p 123 -pctspare 20 -L -busyat 200 -rxpck 2000 -rxbind
- parm /usr/afs/bin/volserver -p 127 -log -rxbind
+ parm /usr/afs/bin/fileserver -p 123 -L -busyat 200 -rxpck 2000 -cb 4000000
+ parm /usr/afs/bin/volserver -p 127 -log
parm /usr/afs/bin/salvager -parallel all32
end
Since an additional component was required for the demand-attach file-server, a new `bnode` type ( `dafs`) is required. The definition should be similar to
bnode dafs dafs 1
- parm /usr/afs/bin/fileserver -p 123 -pctspare 20 -L -busyat 50 -rxpck 2000 -rxbind -cb 4000000 -vattachpar 128 -vlruthresh 1440 -vlrumax 8 -vhashsize 11
- parm /usr/afs/bin/volserver -p 64 -log -rxbind
+ parm /usr/afs/bin/dafileserver -p 123 -L -busyat 200 -rxpck 2000 -cb 4000000 -vattachpar 128 -vlruthresh 1440 -vlrumax 8 -vhashsize 11
+ parm /usr/afs/bin/davolserver -p 64 -log
parm /usr/afs/bin/salvageserver
- parm /usr/afs/bin/salvager -parallel all32
+ parm /usr/afs/bin/dasalvager -parallel all32
end
-The instance for a demand-attach file-server is therefore `dafs` instead of `fs`.
+The instance for a demand-attach file-server is therefore `dafs`
+instead of `fs`. For a complete list of configuration options see the
+[dafileserver man page](http://docs.openafs.org/Reference/8/dafileserver.html).
-### <a name="File-server Start-up / Shutdown"></a><a name="File-server Start-up / Shutdown "></a> File-server Start-up / Shutdown Sequence
+### <a name="File-server Start-up / Shutdown "></a> File-server Start-up / Shutdown Sequence
The table below compares the start-up sequence for a traditional file-server and a demand-attach file-server.
</tr>
<tr>
<td> </td>
- <td> %BULLET% host / callback state restored </td>
+ <td> host / callback state restored </td>
</tr>
<tr>
<td> </td>
- <td> %BULLET% host / callback state consistency verified </td>
+ <td> host / callback state consistency verified </td>
</tr>
<tr>
- <td> %BULLET% build vice partition list </td>
- <td> %BULLET% build vice partition list </td>
+ <td> build vice partition list </td>
+ <td> build vice partition list </td>
</tr>
<tr>
- <td> %BULLET% volumes are attached </td>
- <td> %BULLET% volume headers read </td>
+ <td> volumes are attached </td>
+ <td> volume headers read </td>
</tr>
<tr>
<td> </td>
- <td> %BULLET% volumes placed into <em>pre-attached</em> state </td>
+ <td> volumes placed into <em>pre-attached</em> state </td>
</tr>
</table>
<th bgcolor="#99CCCC"><strong> Demand-Attach </strong></th>
</tr>
<tr>
- <td> %BULLET% break callbacks </td>
- <td> %BULLET% quiesce host / callback state </td>
+ <td> break callbacks </td>
+ <td> quiesce host / callback state </td>
</tr>
<tr>
- <td> %BULLET% shutdown volumes </td>
- <td> %BULLET% shutdown on-line volumes </td>
+ <td> shutdown volumes </td>
+ <td> shutdown on-line volumes </td>
</tr>
<tr>
<td> </td>
- <td> %BULLET% verify host / callback state consistency </td>
+ <td> verify host / callback state consistency </td>
</tr>
<tr>
<td> </td>
- <td> %BULLET% save host / callback state </td>
+ <td> save host / callback state </td>
</tr>
</table>
On a traditional file-server, volumes are off-lined (detached) serially. In demand-attach, as many threads as possible are used to detach volumes, which is possible due to the notion of a volume has an associated state.
-### <a name="Volume Finite-State Automata"></a> Volume Finite-State Automata
+### Volume Finite-State Automata
The volume finite-state automata is available in the source tree under `doc/arch/dafs-fsa.dot`. See [[=fssync-debug=|DemandAttach#fssync_debug]] for information on debugging the volume package.
-<a name="VolumeLeastRecentlyUsed"></a>
-### <a name="Volume Least Recently Used (VLRU"></a> Volume Least Recently Used (VLRU) Queues
+
+### Volume Least Recently Used (VLRU) Queues
The Volume Least Recently Used (VLRU) is a garbage collection facility which automatically off-lines volumes in the background. The purpose of this facility is to pro-actively off-line infrequently used volumes to improve shutdown and salvage times. The process of off-lining a volume from the "attached" state to the "pre-attached" state is called soft detachment.
The state of the various VLRU queues is dumped with the file-server state and at shutdown.
-<a name="VLRUStateTransitions"></a> The VLRU queues new, mid (intermediate) and old are generational queues for active volumes. State transitions are controlled by inactivity timers and are
+ The VLRU queues new, mid (intermediate) and old are generational queues for active volumes. State transitions are controlled by inactivity timers and are
<table border="1" cellpadding="0" cellspacing="0">
<tr>
`vlruthresh` has been optimized for RO file-servers, where volumes are frequently accessed once a day and soft-detaching has little effect (RO volumes are not salvaged; one of the main reasons for soft detaching).
-### <a name="Vnode Finite-State Automata"></a> Vnode Finite-State Automata
+### Vnode Finite-State Automata
The vnode finite-state automata is available in the source tree under `doc/arch/dafs-vnode-fsa.dot`
-`/usr/afs/bin/fssync-debug` provides low-level inspection and control of the file-server volume package. \*Indiscriminate use of <code>**fsync-debug**</code> can lead to extremely bad things occurring. Use with care. %ENDCOLOR%
+`/usr/afs/bin/fssync-debug` provides low-level inspection and control of the file-server volume package. **Indiscriminate use of <code>fsync-debug</code>** can lead to extremely bad things occurring. Use with care.
-<a name="SalvageServer"></a>
-### <a name="Demand Salvaging"></a> Demand Salvaging
+
+### Demand Salvaging
Demand salvaging is implemented by the `salvageserver`. The actual code for salvaging a volume remains largely unchanged. However, the method for invoking salvaging with demand-attach has changed:
- file-server automatically requests volumes be salvaged as required, i.e. they are marked as requiring salvaging when attached.
- manual initiation of salvaging may be required when access is through the `volserver` (may be addressed at some later date).
-- `bos salvage` requires the `-forceDAFS` flag to initiate salvaging wit DAFS. However, %RED% **salvaging should not be initiated using this method**.%ENDCOLOR%
+- `bos salvage` requires the `-forceDAFS` flag to initiate salvaging with DAFS. However, **salvaging should not be initiated using this method**.
- infinite salvage, attach, salvage, ... loops are possible. There is therefore a hard-limit on the number of times a volume will be salvaged which is reset when the volume is removed or the file-server is restarted.
- volumes are salvaged in parallel and is controlled by the `-Parallel` argument to the `salvageserver`. Defaults to 4.
- the `salvageserver` and the `inode` file-server are incompatible:
- because volumes are inter-mingled on a partition (rather than being separated), a lock for the entire partition on which the volume is located is held throughout. Both the `fileserver` and `volserver` will block if they require this lock, e.g. to restore / dump a volume located on the partition.
- inodes for a particular volume can be located anywhere on a partition. Salvaging therefore results in **every** inode on a partition having to be read to determine whether it belongs to the volume. This is extremely I/O intensive and leads to horrendous salvaging performance.
-- `/usr/afs/bin/salvsync-debug` provides low-level inspection and control over the `salvageserver`. %RED% **Indiscriminate use of `salvsync-debug` can lead to extremely bad things occurring. Use with care.** %ENDCOLOR%
+- `/usr/afs/bin/salvsync-debug` provides low-level inspection and control over the `salvageserver`. **Indiscriminate use of `salvsync-debug` can lead to extremely bad things occurring. Use with care.**
- See [[=salvsync-debug=|DemandAttach#salvsync_debug]] for information on debugging problems with the salvageserver.
-<a name="FSStateDat"></a>
-### <a name="File-Server Host / Callback Stat"></a> File-Server Host / Callback State
+
+### File-Server Host / Callback State
Host / callback information is persistent across restarts with demand-attach. On shutdown, the file-server writes the data to `/usr/afs/local/fsstate.dat`. The contents of this file are read and verified at start-up and hence it is unnecessary to break callbacks on shutdown with demand-attach.
The contents of `fsstate.dat` can be inspected using `/usr/afs/bin/state_analyzer`.
-## <a name="File-Server Arguments (relating"></a><a name="File-Server Arguments (relating "></a> File-Server Arguments (relating to Demand-Attach)
+## <a name="File-Server Arguments (relating "></a> File-Server Arguments (relating to Demand-Attach)
These are available in the man-pages (section 8) for the fileserver; some details are provided here for convenience:
</tr>
<tr>
<td><code>fs-state-verify</code></td>
- <td><none %vbar%="%VBAR%" %vbar^%="%VBAR^%" both="both" restore="restore" save="save"> </none></td>
+ <td> n/a </td>
<td> both </td>
<td> - </td>
<td> Controls the behavior of the state verification mechanism. Before saving or restoring the <code>fileserver</code> state information, the internal host and callback data structures are verified. A value of 'none' turns off all verification. A value of 'save' only performs the verification steps prior to saving state to disk. A value of 'restore' only performs the verification steps after restoring state from disk. A value of 'both' performs all verification steps both prior to saving and after restoring state. </td>
</tr>
</table>
-Arguments controlling the [[VLRU:|Main/WebHome#VolumeLeastRecentlyUsed]]
+Arguments controlling the VLRU
<table border="1" cellpadding="0" cellspacing="0">
<tr>
</tr>
</table>
-## <a name="Tools for Debugging Demand-Attac"></a> Tools for Debugging Demand-Attach File-Server
+## Tools for Debugging Demand-Attach File-Server
Several tools aid debugging problems with demand-attach file-servers. They operate at an extremely low-level and hence require a detailed knowledge of the architecture / code.
-### <a name="==fssync-debug=="></a> <code>**fssync-debug**</code>
+### <code>**fssync-debug**</code>
-%RED% **Indiscriminate use of `fssync-debug` can have extremely dire consequences. Use with care** %ENDCOLOR%
+**Indiscriminate use of `fssync-debug` can have extremely dire consequences. Use with care.**
`fssync-debug` provides low-level inspection and control over the volume package of the file-server. It can be used to display the file-server information associated with a volume, e.g.
An understanding of the [volume finite-state machine](http://www.dementia.org/twiki//view/dafs-fsa.png) is required before the state of a volume should be manipulated.
-### <a name="==salvsync-debug=="></a> <code>**salvsync-debug**</code>
+### <code>**salvsync-debug**</code>
-%RED% **Indiscriminate use of `salvsync-debug` can have extremely dire consequences. Use with care** %ENDCOLOR%
+**Indiscriminate use of `salvsync-debug` can have extremely dire consequences. Use with care**
`salvsync-debug` provides low-level inspection and control of the salvageserver process, including the scheduling order of volumes.
This is the method that should be used on demand-attach file-servers to initiate the manual salvage of volumes. It should be used with care.
-Under normal circumstances, the priority ( `prio`) of a salvage request is the number of times the volume has been requested by clients. %RED% Modifying the priority (and hence the order volumes are salvaged) under heavy demand-salvaging usually leads to extremely bad things happening. %ENDCOLOR% To modify the priority of a request, use
+Under normal circumstances, the priority ( `prio`) of a salvage request is the number of times the volume has been requested by clients. Modifying the priority (and hence the order volumes are salvaged) under heavy demand-salvaging usually leads to extremely bad things happening. To modify the priority of a request, use
salvsync-debug priority -vol 537119916 -part /vicepb -priority 999999
(where `priority` is a 32-bit integer).
-### <a name="==state_analyzer=="></a> <code>**state\_analyzer**</code>
+### <code>**state\_analyzer**</code>
`state_analyzer` allows the contents of the host / callback state file ( `/usr/afs/local/fsstate.dat`) to be inspected.
-#### <a name="Header Information"></a> Header Information
+#### Header Information
Header information is gleaned through the `hdr` command
}
fs state analyzer>
-#### <a name="Host Information"></a> Host Information
+#### Host Information
Host information can be gleaned through the `h` command, e.g.
}
fs state analyzer: h(1)>
-#### <a name="Callback Information"></a> Callback Information
+#### Callback Information
Callback information is available through the `cb` command, e.g.
git://git.openafs.org / openafs-wiki.git / blobdiff