Recover from disk failure

Kudu nodes can only survive failures of disks on which certain Kudu directories are mounted. For more information about the different Kudu directory types, see the Directory configuration topic.

The following table summarizes the resilience to disk failure in different releases of Apache Kudu.

Table 1. Kudu disk failure behavior
Node Type	Kudu directory type	Kudu releases that crash on disk failure
Master	All	All
Tablet Server	Directory containing WALs	All
Tablet Server	Directory containing tablet metadata	All
Tablet Server	Directory containing data blocks only	Pre-1.6.0

When a disk failure occurs that does not lead to a crash, Kudu will stop using the affected directory, shut down tablets with blocks on the affected directories, and automatically 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:

E1205 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

While in this state, the affected node will avoid using the failed disk, leading to lower storage volume and reduced read parallelism. The administrator can remove the failed directory from the --fs_data_dirs gflag to avoid seeing these errors.

When the disk is repaired, remounted, and ready to be reused by Kudu, take the following steps:

Make sure that the Kudu portion of the disk is completely empty.
Stop the tablet server.
Update the --fs_data_dirs gflag to add /data/3, on the server with the disk failure. For example:
```
$ sudo -u kudu kudu fs update_dirs --force --fs_wal_dir=/wals --fs_data_dirs=/data/1,/data/2,/data/3
```
Start the tablet server.
Run ksck to verify cluster health, on any kudu server in the cluster. For example:
```
$ sudo -u kudu kudu cluster ksck master-01.example.com
```