Troubleshoot Object Storage¶

Problem¶

Drive failure can prevent Object Storage performing replication.

Solution¶

In the event that a drive has failed, the first step is to make sure the drive is unmounted. This will make it easier for Object Storage to work around the failure until it has been resolved. If the drive is going to be replaced immediately, then it is just best to replace the drive, format it, remount it, and let replication fill it up.

If you cannot replace the drive immediately, then it is best to leave it unmounted, and remove the drive from the ring. This will allow all the replicas that were on that drive to be replicated elsewhere until the drive is replaced. Once the drive is replaced, it can be re-added to the ring.

You can look at error messages in the /var/log/kern.log file for hints of drive failure.

Problem¶

The server is potentially offline, and may have failed, or require a reboot.

Solution¶

If a server is having hardware issues, it is a good idea to make sure the Object Storage services are not running. This will allow Object Storage to work around the failure while you troubleshoot.

If the server just needs a reboot, or a small amount of work that should only last a couple of hours, then it is probably best to let Object Storage work around the failure and get the machine fixed and back online. When the machine comes back online, replication will make sure that anything that is missing during the downtime will get updated.

If the server has more serious issues, then it is probably best to remove all of the server’s devices from the ring. Once the server has been repaired and is back online, the server’s devices can be added back into the ring. It is important that the devices are reformatted before putting them back into the ring as it is likely to be responsible for a different set of partitions than before.

Problem¶

When drives fail, it can be difficult to detect that a drive has failed, and the details of the failure.

Solution¶

It has been our experience that when a drive is about to fail, error messages appear in the /var/log/kern.log file. There is a script called swift-drive-audit that can be run via cron to watch for bad drives. If errors are detected, it will unmount the bad drive, so that Object Storage can work around it. The script takes a configuration file with the following settings:

Problem¶

An emergency might prevent a successful backup from restoring the cluster to operational status.

Solution¶

You should always keep a backup of swift ring builder files. However, if an emergency occurs, this procedure may assist in returning your cluster to an operational state.

Using existing swift tools, there is no way to recover a builder file from a ring.gz file. However, if you have a knowledge of Python, it is possible to construct a builder file that is pretty close to the one you have lost.

1. Load the ring and a new ringbuilder object in a Python REPL:

   >>> from swift.common.ring import RingData, RingBuilder
   >>> ring = RingData.load('/path/to/account.ring.gz')
   

2. Start copying the data we have in the ring into the builder:

   >>> import math
   >>> partitions = len(ring._replica2part2dev_id[0])
   >>> replicas = len(ring._replica2part2dev_id)
   
   >>> builder = RingBuilder(int(math.log(partitions, 2)), replicas, 1)
   >>> builder.devs = ring.devs
   >>> builder._replica2part2dev = ring._replica2part2dev_id
   >>> builder._last_part_moves_epoch = 0
   >>> from array import array
   >>> builder._last_part_moves = array('B', (0 for _ in xrange(partitions)))
   >>> builder._set_parts_wanted()
   >>> for d in builder._iter_devs():
               d['parts'] = 0
   >>> for p2d in builder._replica2part2dev:
               for dev_id in p2d:
                   builder.devs[dev_id]['parts'] += 1
   
   This is the extent of the recoverable fields.
   

3. For min_part_hours you either have to remember what the value you used was, or just make up a new one:

   >>> builder.change_min_part_hours(24) # or whatever you want it to be
   

4. Validate the builder. If this raises an exception, check your previous code:

   >>> builder.validate()
   

5. After it validates, save the builder and create a new account.builder:

   >>> import pickle
   >>> pickle.dump(builder.to_dict(), open('account.builder', 'wb'), protocol=2)
   >>> exit ()
   

6. You should now have a file called account.builder in the current working directory. Run swift-ring-builder account.builder write_ring and compare the new account.ring.gz to the account.ring.gz that you started from. They probably are not byte-for-byte identical, but if you load them in a REPL and their _replica2part2dev_id and devs attributes are the same (or nearly so), then you are in good shape.

7. Repeat the procedure for container.ring.gz and object.ring.gz, and you might get usable builder files.