Replace EBS volumes of a Kafka installation

Enlarging AWS EBS volumes is very easy and straight-forward. It is however not possible to decrease the size of the volume.

The performance of EBS volumes is strictly related to the size of the disks: bigger disks get higher I/O throughput. So it might be easy to speed up kafka doing I/O intensive work (like reindexing) by temporarily increasing the disk size.

We want to decrease the disks when Kafka is running normal again, because we don’t need the extra storage for now and want to avoid the extra cost for it. Problem is that when you want to decrease the volume of an EBS disk, you have to replace it with a new one. Here is how you do that:

  1. Create a new EBS volume and attach it to the kafka broker machine.
  2. Check with lsblk the new disk device
      $ lsblk
      xvdc    202:32   0    2T  0 disk /kafka-data2
      xvdf    202:80   0  500G  0 disk /kafka-data1
      xvdg    202:96   0  500G  0 disk 
  3. Prepare it with the right filesystem sudo mkfs -t xfs /dev/xvdg
  4. Make a mount point on the broker sudo mkdir /kafka-data3
  5. Mount the disk on the broker sudo mount /dev/xvdg /kafka-data3
  6. Gracefully stop kafka sudo supervisorctl stop kafka
  7. Check if the .kafka_cleanshutdown file is in the data directory. It is placed by Kafka only when a shutdown succeeded. If it is not there, kafka will reindex all files at restart which will take some time. (And might impact the disk’s burst balance.)
  8. Copy the data of the old ebs volume to the new one. rsync -av /kafka-data1/* /kafka-data3. This will take a while. Optionally you can enable the --checksum flag, but this will have a performance impact.
  9. Explicitly copy the cleanshutdown flag as it is not copied by the rsync command. cp /kafka-data1/.kafka_cleanshutdown /kafka-data3
  10. Swap the mount points
     sudo umount /kafka-data1
     sudo umount /kafka-data3
     sudo mount /dev/xvdg /kafka-data1
  11. Restart Kafka sudo supervisorctl start kafka