Updating ServerConfiguration doc.

Topology service was the old syntax.
Added a section on directory configuration.

doc/ScalabilityPhilosophy.md

@@ -139,9 +139,8 @@ available and consistent data store.
 
 Lock servers were built for this exact purpose, and Vitess needs one such
 cluster to be setup to run smoothly. Vitess can be customized to utilize any
-lock server, and by default it supports zookeeper and etcd. We call this
-component
-[Topology Service](/user-guide/topology-service.html).
+lock server, and by default it supports Zookeeper, etcd and Consul. We call this
+component [Topology Service](/user-guide/topology-service.html).
 
 As Vitess is meant to run in multiple data centers / regions (called cells
 below), it relies on two different lock servers:

doc/ServerConfiguration.md

@@ -177,18 +177,21 @@ See the
 for more information on how to setup both of these features, and what command
 line parameters exist.
 
-## Lock server configuration
+## Topology Service configuration
 
-Vttablet, vtgate, vtctld need the right command line parameters to find the topo server. First the *topo\_implementation* flag needs to be set to one of *zookeeper* or *etcd*. Then each is configured as follows:
+Vttablet, vtgate, vtctld need the right command line parameters to find the
+Topology Server. First the *topo\_implementation* flag needs to be set to one of
+*zk2*, *etcd2*, or *consul*. Then they're all configured as follows:
 
-* zookeeper: it is configured using the *ZK\_CLIENT\_CONFIG* environment
-  variable, that points at a JSON file that contains the global and local cells
-  configurations. For instance, this can be the contents of the file:
-  ```{"cell1": "server1:port1,server2:port2", "cell2":
-  "server1:port1,server2:port2", "global": "server1:port1,server2:port2"}```
-* etcd: the *etcd\_global\_addrs* parameter needs to point at the global
-  instance. Then inside that global instance, the */vt/cells/<cell name>* path
-  needs to point at each cell instance.
+* The *topo_global_server_address* contains the server address / addresses of
+  the global topology server.
+* The *topo_global_root* contains the directory / path to use.
+
+Note that the local cell for the tablet must exist and be configured properly in
+the Topology Service for vttablet to start. Local cells are configured inside
+the topo server, by using the `vtctl AddCellInfo` command. See
+the [Topology Service](/user-guide/topology-service.html) documentation for more
+information.
 
 ## VTTablet
 
@@ -199,6 +202,41 @@ VTTablet has a large number of command line options. Some important ones will be
 * 2-4 cores (in proportion to MySQL cores)
 * 2-4 GB RAM
 
+### Directory Configuration
+
+vttablet supports a number of command line options and environment variables
+to facilitate its setup.
+
+The **VTDATAROOT** environment variable specifies the toplevel directory for all
+data files. If not set, it defaults to `/vt`.
+
+By default, a vttablet will use a subdirectory in **VTDATAROOT** named
+`vt_NNNNNNNNNN` where `NNNNNNNNNN` is the tablet id. The **tablet_dir**
+command-line parameter allows overriding this relative path. This is useful in
+containers where the filesystem only contains one vttablet, in order to have a
+fixed root directory.
+
+When starting up and using `mysqlctl` to manage MySQL, the MySQL files will be
+in subdirectories of the tablet root. For instance, `bin-logs` for the binary
+logs, `data` for the data files, and `relay-logs` for the relay logs.
+
+It is possible to host different parts of a MySQL server files on different
+partitions. For instance, the data file may reside in flash, while the bin logs
+and relay logs are on spindle. To achieve this, create a symlink from
+`$VTDATAROOT/<dir name>` to the proper location on disk. When MySQL is
+configured by mysqlctl, it will realize this directory exists, and use it for the
+files it would otherwise have put in the tablet directory. For instance, to host
+the binlogs in `/mnt/bin-logs`:
+
+* Create a symlink from `$VTDATAROOT/bin-logs` to `/mnt/bin-logs`.
+
+* When starting up a tablet:
+
+  * `/mnt/bin-logs/vt_NNNNNNNNNN` will be created.
+
+  * `$VTDATAROOT/vt_NNNNNNNNNN/bin-logs` will be a symlink to
+    `/mnt/bin-logs/vt_NNNNNNNNNN`
+
 ### Initialization
 
 * Init_keyspace, init_shard, init_tablet_type: These parameters should be set at startup with the keyspace / shard / tablet type to start the tablet as. Note ‘master’ is not allowed here, instead use ‘replica’, as the tablet when starting will figure out if it is the master (this way, all replica tablets start with the same command line parameters, independently of which one is the master).