Apache Kudu Administration

Kudu is easier to manage with Cloudera Manager than in a standalone installation. See Cloudera’s Kudu documentation for more details about using Kudu with Cloudera Manager.

Starting and Stopping Kudu Processes

These instructions are relevant only when Kudu is installed using operating system packages (e.g. rpm or deb).

  1. Start Kudu services using the following commands:

    $ sudo service kudu-master start
$ sudo service kudu-tserver start

  2. To stop Kudu services, use the following commands:

    $ sudo service kudu-master stop
$ sudo service kudu-tserver stop

Kudu Web Interfaces

Kudu tablet servers and masters expose useful operational information on a built-in web interface,

Kudu Master Web Interface

Kudu master processes serve their web interface on port 8051. The interface exposes several pages with information about the cluster state:

  • A list of tablet servers, their host names, and the time of their last heartbeat.

  • A list of tables, including schema and tablet location information for each.

  • SQL code which you can paste into Impala Shell to add an existing table to Impala’s list of known data sources.

Kudu Tablet Server Web Interface

Each tablet server serves a web interface on port 8050. The interface exposes information about each tablet hosted on the server, its current state, and debugging information about maintenance background operations.

Common Web Interface Pages

Both Kudu masters and tablet servers expose a common set of information via their web interfaces:

  • HTTP access to server logs.

  • an /rpcz endpoint which lists currently running RPCs via JSON.

  • pages giving an overview and detailed information on the memory usage of different components of the process.

  • information on the current set of configuration flags.

  • information on the currently running threads and their resource consumption.

  • a JSON endpoint exposing metrics about the server.

  • information on the deployed version number of the daemon.

These interfaces are linked from the landing page of each daemon’s web UI.

Kudu Metrics

Kudu daemons expose a large number of metrics. Some metrics are associated with an entire server process, whereas others are associated with a particular tablet replica.

Listing available metrics

The full set of available metrics for a Kudu server can be dumped via a special command line flag:

$ kudu-tserver --dump_metrics_json
$ kudu-master --dump_metrics_json

This will output a large JSON document. Each metric indicates its name, label, description, units, and type. Because the output is JSON-formatted, this information can easily be parsed and fed into other tooling which collects metrics from Kudu servers.

Collecting metrics via HTTP

Metrics can be collected from a server process via its HTTP interface by visiting /metrics. The output of this page is JSON for easy parsing by monitoring services. This endpoint accepts several GET parameters in its query string:

  • /metrics?metrics=<substring1>,<substring2>,…​ - limits the returned metrics to those which contain at least one of the provided substrings. The substrings also match entity names, so this may be used to collect metrics for a specific tablet.

  • /metrics?include_schema=1 - includes metrics schema information such as unit, description, and label in the JSON output. This information is typically elided to save space.

  • /metrics?compact=1 - eliminates unnecessary whitespace from the resulting JSON, which can decrease bandwidth when fetching this page from a remote host.

  • /metrics?include_raw_histograms=1 - include the raw buckets and values for histogram metrics, enabling accurate aggregation of percentile metrics over time and across hosts.

For example:

$ curl -s 'http://example-ts:8050/metrics?include_schema=1&metrics=connections_accepted'
[
    {
        "type": "server",
        "id": "kudu.tabletserver",
        "attributes": {},
        "metrics": [
            {
                "name": "rpc_connections_accepted",
                "label": "RPC Connections Accepted",
                "type": "counter",
                "unit": "connections",
                "description": "Number of incoming TCP connections made to the RPC server",
                "value": 92
            }
        ]
    }
]
$ curl -s 'http://example-ts:8050/metrics?metrics=log_append_latency'
[
    {
        "type": "tablet",
        "id": "c0ebf9fef1b847e2a83c7bd35c2056b1",
        "attributes": {
            "table_name": "lineitem",
            "partition": "hash buckets: (55), range: [(<start>), (<end>))",
            "table_id": ""
        },
        "metrics": [
            {
                "name": "log_append_latency",
                "total_count": 7498,
                "min": 4,
                "mean": 69.3649,
                "percentile_75": 29,
                "percentile_95": 38,
                "percentile_99": 45,
                "percentile_99_9": 95,
                "percentile_99_99": 167,
                "max": 367244,
                "total_sum": 520098
            }
        ]
    }
]
All histograms and counters are measured since the server start time, and are not reset upon collection.

Collecting metrics to a log

Kudu may be configured to periodically dump all of its metrics to a local log file using the --metrics_log_interval_ms flag. Set this flag to the interval at which metrics should be written to a log file.

The metrics log will be written to the same directory as the other Kudu log files, with the same naming format. After any metrics log file reaches 64MB uncompressed, the log will be rolled and the previous file will be gzip-compressed.

The log file generated has three space-separated fields. The first field is the word metrics. The second field is the current timestamp in microseconds since the Unix epoch. The third is the current value of all metrics on the server, using a compact JSON encoding. The encoding is the same as the metrics fetched via HTTP described above.

Although metrics logging automatically rolls and compresses previous log files, it does not remove old ones. Since metrics logging can use significant amounts of disk space, consider setting up a system utility to monitor space in the log directory and archive or delete old segments.

Common Kudu workflows

Migrating to Multiple Kudu Masters

For high availability and to avoid a single point of failure, Kudu clusters should be created with multiple masters. Many Kudu clusters were created with just a single master, either for simplicity or because Kudu multi-master support was still experimental at the time. This workflow demonstrates how to migrate to a multi-master configuration.

The workflow is unsafe for adding new masters to an existing multi-master configuration. Do not use it for that purpose.
All of the command line steps below should be executed as the Kudu UNIX user, typically kudu.
The workflow presupposes at least basic familiarity with Kudu configuration management. If using Cloudera Manager (CM), the workflow also presupposes familiarity with it.

Prepare for the migration

  1. Establish a maintenance window (one hour should be sufficient). During this time the Kudu cluster will be unavailable.

  2. Decide how many masters to use. The number of masters should be odd. Three or five node master configurations are recommended; they can tolerate one or two failures respectively.

  3. Perform the following preparatory steps for the existing master:

    • Identify and record the directory where the master’s data lives. If using Kudu system packages, the default value is /var/lib/kudu/master, but it may be customized via the fs_wal_dir and fs_data_dirs configuration parameters. Please note if you’ve set fs_data_dirs to some directories other than the value of fs_wal_dir, it should be explicitly included in every command below where fs_wal_dir is also included. For more information on configuring these directories, see the Kudu Configuration docs.

    • Identify and record the port the master is using for RPCs. The default port value is 7051, but it may have been customized using the rpc_bind_addresses configuration parameter.

    • Identify the master’s UUID. It can be fetched using the following command:

      $ kudu fs dump uuid --fs_wal_dir=<master_wal_dir> [--fs_data_dirs=<master_data_dirs>] 2>/dev/null
      master_data_dir

      existing master’s previously recorded data directory

      Example
      $ kudu fs dump uuid --fs_wal_dir=/var/lib/kudu/master 2>/dev/null
4aab798a69e94fab8d77069edff28ce0

    • Optional: configure a DNS alias for the master. The alias could be a DNS cname (if the machine already has an A record in DNS), an A record (if the machine is only known by its IP address), or an alias in /etc/hosts. The alias should be an abstract representation of the master (e.g. master-1).

      Without DNS aliases it is not possible to recover from permanent master failures without bringing the cluster down for maintenance, and as such, it is highly recommended.

  4. Perform the following preparatory steps for each new master:

    • Choose an unused machine in the cluster. The master generates very little load so it can be colocated with other data services or load-generating processes, though not with another Kudu master from the same configuration.

    • Ensure Kudu is installed on the machine, either via system packages (in which case the kudu and kudu-master packages should be installed), or via some other means.

    • Choose and record the directory where the master’s data will live.

    • Choose and record the port the master should use for RPCs.

    • Optional: configure a DNS alias for the master (e.g. master-2, master-3, etc).

Perform the migration

  1. Stop all the Kudu processes in the entire cluster.

  2. Format the data directory on each new master machine, and record the generated UUID. Use the following command sequence:

    $ kudu fs format --fs_wal_dir=<master_wal_dir> [--fs_data_dirs=<master_data_dirs>]
$ kudu fs dump uuid --fs_wal_dir=<master_wal_dir> [--fs_data_dirs=<master_data_dirs>] 2>/dev/null
    master_data_dir

    new master’s previously recorded data directory

    Example
    $ kudu fs format --fs_wal_dir=/var/lib/kudu/master
$ kudu fs dump uuid --fs_wal_dir=/var/lib/kudu/master 2>/dev/null
f5624e05f40649b79a757629a69d061e

  3. If using CM, add the new Kudu master roles now, but do not start them.

    • If using DNS aliases, override the empty value of the Master Address parameter for each role (including the existing master role) with that master’s alias.

    • Add the port number (separated by a colon) if using a non-default RPC port value.

  4. Rewrite the master’s Raft configuration with the following command, executed on the existing master machine:

    $ kudu local_replica cmeta rewrite_raft_config --fs_wal_dir=<master_wal_dir> [--fs_data_dirs=<master_data_dirs>] <tablet_id> <all_masters>
    master_data_dir

    existing master’s previously recorded data directory

    tablet_id

    must be the string 00000000000000000000000000000000

    all_masters

    space-separated list of masters, both new and existing. Each entry in the list must be a string of the form <uuid>:<hostname>:<port>

    uuid

    master’s previously recorded UUID

    hostname

    master’s previously recorded hostname or alias

    port

    master’s previously recorded RPC port number

    Example
    $ kudu local_replica cmeta rewrite_raft_config --fs_wal_dir=/var/lib/kudu/master 00000000000000000000000000000000 4aab798a69e94fab8d77069edff28ce0:master-1:7051 f5624e05f40649b79a757629a69d061e:master-2:7051 988d8ac6530f426cbe180be5ba52033d:master-3:7051

  5. Modify the value of the master_addresses configuration parameter for both existing master and new masters. The new value must be a comma-separated list of all of the masters. Each entry is a string of the form <hostname>:<port>

    hostname

    master’s previously recorded hostname or alias

    port

    master’s previously recorded RPC port number

  6. Start the existing master.

  7. Copy the master data to each new master with the following command, executed on each new master machine:

    $ kudu local_replica copy_from_remote --fs_wal_dir=<master_wal_dir> [--fs_data_dirs=<master_data_dirs>] <tablet_id> <existing_master>
    master_data_dir

    new master’s previously recorded data directory

    tablet_id

    must be the string 00000000000000000000000000000000

    existing_master

    RPC address of the existing master and must be a string of the form <hostname>:<port>

    hostname

    existing master’s previously recorded hostname or alias

    port

    existing master’s previously recorded RPC port number

    Example
    $ kudu local_replica copy_from_remote --fs_wal_dir=/var/lib/kudu/master 00000000000000000000000000000000 master-1:7051

  8. Start all of the new masters.

    Skip the next step if using CM.

  9. Modify the value of the tserver_master_addrs configuration parameter for each tablet server. The new value must be a comma-separated list of masters where each entry is a string of the form <hostname>:<port>

    hostname

    master’s previously recorded hostname or alias

    port

    master’s previously recorded RPC port number

  10. Start all of the tablet servers.

Congratulations, the cluster has now been migrated to multiple masters! To verify that all masters are working properly, consider performing the following sanity checks:

  • Using a browser, visit each master’s web UI. Look at the /masters page. All of the masters should be listed there with one master in the LEADER role and the others in the FOLLOWER role. The contents of /masters on each master should be the same.

  • Run a Kudu system check (ksck) on the cluster using the kudu command line tool. See Checking Cluster Health with ksck for more details.

Recovering from a dead Kudu Master in a Multi-Master Deployment

Kudu multi-master deployments function normally in the event of a master loss. However, it is important to replace the dead master; otherwise a second failure may lead to a loss of availability, depending on the number of available masters. This workflow describes how to replace the dead master.

Due to KUDU-1620, it is not possible to perform this workflow without also restarting the live masters. As such, the workflow requires a maintenance window, albeit a potentially brief one if the cluster was set up with DNS aliases.

Kudu does not yet support live Raft configuration changes for masters. As such, it is only possible to replace a master if the deployment was created with DNS aliases or if every node in the cluster is first shut down. See the multi-master migration workflow for more details on deploying with DNS aliases.
The workflow presupposes at least basic familiarity with Kudu configuration management. If using Cloudera Manager (CM), the workflow also presupposes familiarity with it.
All of the command line steps below should be executed as the Kudu UNIX user, typically kudu.

Prepare for the recovery

  1. If the deployment was configured without DNS aliases perform the following steps:

    • Establish a maintenance window (one hour should be sufficient). During this time the Kudu cluster will be unavailable.

    • Shut down all Kudu tablet server processes in the cluster.

  2. Ensure that the dead master is well and truly dead. Take whatever steps needed to prevent it from accidentally restarting; this can be quite dangerous for the cluster post-recovery.

  3. Choose one of the remaining live masters to serve as a basis for recovery. The rest of this workflow will refer to this master as the "reference" master.

  4. Choose an unused machine in the cluster where the new master will live. The master generates very little load so it can be colocated with other data services or load-generating processes, though not with another Kudu master from the same configuration. The rest of this workflow will refer to this master as the "replacement" master.

  5. Perform the following preparatory steps for the replacement master:

    • Ensure Kudu is installed on the machine, either via system packages (in which case the kudu and kudu-master packages should be installed), or via some other means.

    • Choose and record the directory where the master’s data will live.

  6. Perform the following preparatory steps for each live master:

    • Identify and record the directory where the master’s data lives. If using Kudu system packages, the default value is /var/lib/kudu/master, but it may be customized via the fs_wal_dir and fs_data_dirs configuration parameters. Please note if you’ve set fs_data_dirs to some directories other than the value of fs_wal_dir, it should be explicitly included in every command below where fs_wal_dir is also included. For more information on configuring these directories, see the Kudu Configuration docs.

    • Identify and record the master’s UUID. It can be fetched using the following command:

      $ kudu fs dump uuid --fs_wal_dir=<master_wal_dir> [--fs_data_dirs=<master_data_dirs>] 2>/dev/null
      master_data_dir

      live master’s previously recorded data directory

      Example
      $ kudu fs dump uuid --fs_wal_dir=/var/lib/kudu/master 2>/dev/null
80a82c4b8a9f4c819bab744927ad765c

  7. Perform the following preparatory steps for the reference master:

    • Identify and record the directory where the master’s data lives. If using Kudu system packages, the default value is /var/lib/kudu/master, but it may be customized via the fs_wal_dir and fs_data_dirs configuration parameters. Please note if you’ve set fs_data_dirs to some directories other than the value of fs_wal_dir, it should be explicitly included in every command below where fs_wal_dir is also included. For more information on configuring these directories, see the Kudu Configuration docs.

    • Identify and record the UUIDs of every master in the cluster, using the following command:

      $ kudu local_replica cmeta print_replica_uuids --fs_wal_dir=<master_wal_dir> [--fs_data_dirs=<master_data_dirs>] <tablet_id> 2>/dev/null
      master_data_dir

      reference master’s previously recorded data directory

      tablet_id

      must be the string 00000000000000000000000000000000

      Example
      $ kudu local_replica cmeta print_replica_uuids --fs_wal_dir=/var/lib/kudu/master 00000000000000000000000000000000 2>/dev/null
80a82c4b8a9f4c819bab744927ad765c 2a73eeee5d47413981d9a1c637cce170 1c3f3094256347528d02ec107466aef3

  8. Using the two previously-recorded lists of UUIDs (one for all live masters and one for all masters), determine and record (by process of elimination) the UUID of the dead master.

Perform the recovery

  1. Format the data directory on the replacement master machine using the previously recorded UUID of the dead master. Use the following command sequence:

    $ kudu fs format --fs_wal_dir=<master_wal_dir> [--fs_data_dirs=<master_data_dirs>] --uuid=<uuid>
    master_data_dir

    replacement master’s previously recorded data directory

    uuid

    dead master’s previously recorded UUID

    Example
    $ kudu fs format --fs_wal_dir=/var/lib/kudu/master --uuid=80a82c4b8a9f4c819bab744927ad765c

  2. Copy the master data to the replacement master with the following command:

    $ kudu local_replica copy_from_remote --fs_wal_dir=<master_wal_dir> [--fs_data_dirs=<master_data_dirs>] <tablet_id> <reference_master>
    master_data_dir

    replacement master’s previously recorded data directory

    tablet_id

    must be the string 00000000000000000000000000000000

    reference_master

    RPC address of the reference master and must be a string of the form <hostname>:<port>

    hostname

    reference master’s previously recorded hostname or alias

    port

    reference master’s previously recorded RPC port number

    Example
    $ kudu local_replica copy_from_remote --fs_wal_dir=/var/lib/kudu/master 00000000000000000000000000000000 master-2:7051

  3. If using CM, add the replacement Kudu master role now, but do not start it.

    • Override the empty value of the Master Address parameter for the new role with the replacement master’s alias.

    • Add the port number (separated by a colon) if using a non-default RPC port value.

  4. If the cluster was set up with DNS aliases, reconfigure the DNS alias for the dead master to point at the replacement master.

  5. If the cluster was set up without DNS aliases, perform the following steps:

    • Stop the remaining live masters.

    • Rewrite the Raft configurations on these masters to include the replacement master. See Step 4 of Perform the Migration for more details.

  6. Start the replacement master.

  7. Restart the remaining masters in the new multi-master deployment. While the masters are shut down, there will be an availability outage, but it should last only as long as it takes for the masters to come back up.

Congratulations, the dead master has been replaced! To verify that all masters are working properly, consider performing the following sanity checks:

  • Using a browser, visit each master’s web UI. Look at the /masters page. All of the masters should be listed there with one master in the LEADER role and the others in the FOLLOWER role. The contents of /masters on each master should be the same.

  • Run a Kudu system check (ksck) on the cluster using the kudu command line tool. See Checking Cluster Health with ksck for more details.

Removing Kudu Masters from a Multi-Master Deployment

In the event that a multi-master deployment has been overallocated nodes, the following steps should be taken to remove the unwanted masters.

In planning the new multi-master configuration, keep in mind that the number of masters should be odd and that three or five node master configurations are recommended.
Dropping the number of masters below the number of masters currently needed for a Raft majority can incur data loss. To mitigate this, ensure that the leader master is not removed during this process.

Prepare for the removal

  1. Establish a maintenance window (one hour should be sufficient). During this time the Kudu cluster will be unavailable.

  2. Identify the UUID and RPC address current leader of the multi-master deployment by visiting the /masters page of any master’s web UI. This master must not be removed during this process; its removal may result in severe data loss.

  3. Stop all the Kudu processes in the entire cluster.

  4. If using CM, remove the unwanted Kudu master.

Perform the removal

  1. Rewrite the Raft configuration on the remaining masters to include only the remaining masters. See Step 4 of Perform the Migration for more details.

  2. Remove the data directories and WAL directory on the unwanted masters. This is a precaution to ensure that they cannot start up again and interfere with the new multi-master deployment.

  3. Modify the value of the master_addresses configuration parameter for the masters of the new multi-master deployment. If migrating to a single-master deployment, the master_addresses flag should be omitted entirely.

  4. Start all of the masters that were not removed.

  5. Modify the value of the tserver_master_addrs configuration parameter for the tablet servers to remove any unwanted masters.

  6. Start all of the tablet servers.

Congratulations, the masters have now been removed! To verify that all masters are working properly, consider performing the following sanity checks:

  • Using a browser, visit each master’s web UI. Look at the /masters page. All of the masters should be listed there with one master in the LEADER role and the others in the FOLLOWER role. The contents of /masters on each master should be the same.

  • Run a Kudu system check (ksck) on the cluster using the kudu command line tool. See Checking Cluster Health with ksck for more details.

Checking Cluster Health with ksck

The kudu CLI includes a tool named ksck which can be used for checking cluster health and data integrity. ksck will identify issues such as under-replicated tablets, unreachable tablet servers, or tablets without a leader.

ksck should be run from the command line, and requires the full list of master addresses to be specified:

$ kudu cluster ksck master-01.example.com,master-02.example.com,master-03.example.com

To see a full list of the options available with ksck, use the --help flag. If the cluster is healthy, ksck will print a success message, and return a zero (success) exit status.

Connected to the Master
Fetched info from all 1 Tablet Servers
Table IntegrationTestBigLinkedList is HEALTHY (1 tablet(s) checked)

The metadata for 1 table(s) is HEALTHY
OK

If the cluster is unhealthy, for instance if a tablet server process has stopped, ksck will report the issue(s) and return a non-zero exit status:

Connected to the Master
WARNING: Unable to connect to Tablet Server 8a0b66a756014def82760a09946d1fce
(tserver-01.example.com:7050): Network error: could not send Ping RPC to server: Client connection negotiation failed: client connection to 192.168.0.2:7050: connect: Connection refused (error 61)
WARNING: Fetched info from 0 Tablet Servers, 1 weren't reachable
Tablet ce3c2d27010d4253949a989b9d9bf43c of table 'IntegrationTestBigLinkedList'
is unavailable: 1 replica(s) not RUNNING
  8a0b66a756014def82760a09946d1fce (tserver-01.example.com:7050): TS unavailable [LEADER]

  Table IntegrationTestBigLinkedList has 1 unavailable tablet(s)

  WARNING: 1 out of 1 table(s) are not in a healthy state
  ==================
  Errors:
  ==================
  error fetching info from tablet servers: Network error: Not all Tablet Servers are reachable
  table consistency check error: Corruption: 1 table(s) are bad

  FAILED
  Runtime error: ksck discovered errors

To verify data integrity, the optional --checksum_scan flag can be set, which will ensure the cluster has consistent data by scanning each tablet replica and comparing results. The --tables or --tablets flags can be used to limit the scope of the checksum scan to specific tables or tablets, respectively. For example, checking data integrity on the IntegrationTestBigLinkedList table can be done with the following command:

$ kudu cluster ksck --checksum_scan --tables IntegrationTestBigLinkedList master-01.example.com,master-02.example.com,master-03.example.com

Changing Directory Configurations

For higher read parallelism and larger volumes of storage per server, users may want to configure servers to store data in multiple directories on different devices. Once a server is started, users must go through the following steps to change the directory configuration.

Adding a Data Directory

Users can add data directories to an existing master or tablet server via the kudu fs update_dirs tool. Data is striped across data directories, and when a new data directory is added, new data will be striped across the union of the old and new directories.

Only new tablet replicas (i.e. brand new tablets' replicas and replicas that are copied to the server for high availability) will use the new directory. Existing tablet replicas on the server will not be rebalanced across the new directory.
The first configured data directory on a server contains the metadata files for all tablets on that server. Kudu will not permit reordering of this "metadata directory". For example if a cluster is configured with /data/1 as the first entry in --fs_data_dirs, all further configurations must be formatted as /data/1,<new directories>.
All of the command line steps below should be executed as the Kudu UNIX user, typically kudu.

  1. The tool can only run while the server is offline, so establish a maintenance window to update the server. The tool itself runs quickly, so this offline window should be brief, and as such, only the server to update needs to be offline. However, if the server is offline for too long (see the follower_unavailable_considered_failed_sec flag), the tablet replicas on it may be evicted from their Raft groups. To avoid this, it may be desirable to bring the entire cluster offline while performing the update.

  2. Run the tool with the desired directory configuration flags. For example, if a cluster was set up with --fs_wal_dir=/wals and --fs_data_dirs=/data/1,/data2 and a new /data/3 is desired, run the command:

    $ kudu fs update_dirs --fs_wal_dir=/wals --fs_data_dirs=/data/1,/data/2,/data/3

  3. Modify the values of the fs_wal_dir and fs_data_dirs flags for the updated sever. If using CM, make sure to only update the configurations of the updated server, rather than of the entire Kudu service.

  4. Once complete, the server process can be started. When Kudu is installed using system packages, service is typically used:

    $ sudo service kudu-tserver start

Rebuilding a Kudu Filesystem Layout

Kudu does not allow for the removal of directories, or for any changes to the write-ahead-log (WAL) directory or metadata directory. In order to start a server with such directory configuration changes, the WAL and data directories on the server must be deleted and rebuilt, destroying the copy of the data for each tablet replica hosted on the local server. Kudu will automatically re-replicate tablet replicas removed in this way, provided the replication factor is at least three and all other servers are online and healthy.

These steps use a tablet server as an example, but the steps are the same for Kudu master servers.
Before proceeding, ensure the contents of the directories are backed up, either as a copy or in the form of other tablet replicas.

  1. The first step to rebuilding a server with a new directory configuration is emptying all of the server’s existing directories. For example, if a tablet server is configured with --fs_wal_dir=/data/0/kudu-tserver-wal and --fs_data_dirs=/data/1/kudu-tserver,/data/2/kudu-tserver, the following commands will remove the WAL directory’s and data directories' contents:

    # Note: this will delete all of the data from the local tablet server.
$ rm -rf /data/0/kudu-tserver-wal/* /data/1/kudu-tserver/* /data/2/kudu-tserver/*

  2. If using CM, update the configurations for the rebuilt server to include only the desired directories. Make sure to only update the configurations of servers to which changes were applied, rather than of the entire Kudu service.

  3. After the WAL and data directories are deleted, the server process can be started with the new directory configuration. The appropriate sub-directories will be created by Kudu upon starting up.

Recovering from Disk Failure

As of Kudu 1.6.0, Kudu master servers are not resilient to any types of disk failures. Kudu tablet servers are only resilient to disk failures if they occur on a disk storing only data blocks, so the failure of a disk where the write-ahead logs or tablet metadata are stored will result in a crash of the entire tablet server.

Failures in failure-intolerant directories will lead to a crash, upon which the server must be rebuilt, replacing or removing the failed disk from Kudu’s configuration. See the section on Rebuilding a Kudu Filesystem Layout for more details.

In the case of a failure in a failure-tolerant directory, Kudu will automatically stop using the affected disk, shut down tablets with blocks on the affected disk, and re-replicate the affected tablets to other tablet servers. The affected server will remain alive and print messages to the log indicating the disk failure, for example:

E1025 19:06:24.163748 27115 data_dirs.cc:1011] Directory /data/8/kudu/data marked as failed
E1205 19:06:30.324795 27064 log_block_manager.cc:1822] Not using report from /data/8/kudu/data: IO error: Could not open container 0a6283cab82d4e75848f49772d2638fe: /data/8/kudu/data/0a6283cab82d4e75848f49772d2638fe.metadata: Read-only file system (error 30)
E1205 19:06:33.564638 27220 ts_tablet_manager.cc:946] T 4957808439314e0d97795c1394348d80 P 70f7ee61ead54b1885d819f354eb3405: aborting tablet bootstrap: tablet has data in a failed directory