20 Ceph Interview Questions and Answers

Ceph is a software-defined storage platform that is popular among developers and DevOps professionals. When interviewing for a position that uses Ceph, it is important to be prepared to answer questions about your experience and knowledge of the platform. This article reviews some of the most common Ceph interview questions and provides tips on how to answer them.

Ceph Interview Questions and Answers

Here are 20 commonly asked Ceph interview questions and answers to prepare you for your interview:

1. What is Ceph?

Ceph is a free software storage platform that offers object, block, and file system storage in a single unified storage cluster. Ceph is designed to provide high performance, scalability, and reliability while being easy to deploy and manage.

2. Can you explain how the OSD daemon works in Ceph?

The OSD daemon is responsible for storing data on a Ceph cluster. It handles data replication and recovery, and is responsible for communicating with other OSD daemons in the cluster to maintain data consistency.

3. How does Ceph handle failures and recoveries of OSDs?

Ceph OSDs are designed to be self-healing in the event of failures. When an OSD fails, the Ceph cluster will automatically detect the failure and begin the process of re-replicating the data that was stored on the failed OSD. This process ensures that data is always available and that the Ceph cluster can continue to function even in the event of an OSD failure.

4. Can you explain what CRUSH algorithms do in Ceph?

CRUSH algorithms are used in Ceph to determine how data should be stored and retrieved in a Ceph cluster. CRUSH algorithms take into account factors such as the number of devices in a cluster, the size of each device, and the network topology in order to determine the best way to store and retrieve data. This ensures that data is stored in a way that is both efficient and reliable.

5. What are some use cases for Ceph?

Ceph is a distributed storage system that is designed to provide high performance, reliability, and scalability. Ceph can be used for a variety of different storage needs, such as block storage, object storage, and file storage. Ceph is often used in cloud computing environments and can be used to store data from a variety of different applications.

6. What is a crush map?

A crush map is a data structure that Ceph uses to store information about the physical layout of its storage cluster, including the location of objects and the relationships between different devices. This information is used by the Ceph OSD (Object Storage Daemon) to determine where to store data for optimal performance and reliability.

7. What is an osdmap?

The osdmap is a data structure that Ceph uses to track the state of the storage cluster. It contains information about which OSDs are up and running, as well as their current weight and capacity. The osdmap is used by the Ceph monitors to make decisions about which OSDs to place new data on.

8. Can you explain what an MDS is in context with Ceph?

MDS, or Metadata Server, is a process that runs on each Ceph cluster node. MDS is responsible for storing metadata about the objects stored in the cluster, as well as for providing a namespace for those objects.

9. Can you explain what LVM (Logical Volume Manager) is?

LVM is a system that allows you to manage disk space more efficiently by creating logical volumes. These logical volumes can be created from one or more physical volumes, and can be resized as needed. This can be helpful if you need to increase the size of a particular volume without having to move or copy data to a new location.

10. What is RADOS?

RADOS is the Reliable Autonomic Distributed Object Store, and it is the underlying storage system for Ceph. RADOS provides a scalable, reliable, and self-healing storage platform that is perfect for use in a distributed storage system like Ceph.

11. What is the main difference between HDFS and Ceph?

The main difference between HDFS and Ceph is that Ceph is a distributed file system while HDFS is a centralized file system. Ceph is designed to provide high availability and scalability by replicating data across multiple servers. HDFS, on the other hand, relies on a single server for storing data. This makes Ceph a more reliable option for storing large amounts of data.

12. What’s the primary advantage of using Ceph over other storage solutions like AWS S3 or Azure Blob Storage?

Ceph is an open source solution, which means that it is free to use and modify. This can be a significant advantage over other storage solutions, which can be expensive to use. Additionally, Ceph is a scalable solution, which means that it can grow to meet the needs of a large organization.

13. What is Object Gateway?

Object Gateway is a Ceph object storage feature that provides compatibility with Amazon S3-based applications. It is implemented as a Ceph RADOS gateway, which is a RESTful object storage interface built on top of librados.

14. What types of data can be stored in Ceph?

Ceph is a versatile storage system that can accommodate a wide variety of data types. This includes structured data like databases, unstructured data like images and videos, and even streaming data like audio and video files.

15. What happens to your data if one of the nodes in your cluster goes down?

When a node goes down, the data that was stored on that node is lost. The other nodes in the cluster will continue to function and will be able to serve any data that was stored on the lost node, but any data that was only stored on the lost node will be gone.

16. Does Ceph support compression? If yes, then where is it applied?

Ceph does support compression, and it is applied at the object level. This means that each individual object is compressed, rather than the entire Ceph pool.

17. What is libcephfs?

Libcephfs is a library that provides APIs for accessing the Ceph distributed file system. This library is used by applications that need to interact with Ceph in order to read or write data to the file system.

18. Can you explain what EC (Erasure Coding) pools are?

EC pools are a type of storage pool in Ceph that uses erasure coding to provide data protection. Erasure coding is a method of data storage that breaks data up into smaller pieces and then encodes those pieces with redundant information. This allows for data to be reconstructed even if some of the original pieces are lost or corrupted. EC pools can provide a higher level of data protection than traditional storage pools, but they come at the cost of increased storage overhead and reduced performance.

19. Is there any limit on the number of volumes that can be created in Ceph?

No, there is no limit on the number of volumes that can be created in Ceph.

20. What are RBDs?

RBDs are Ceph’s implementation of block storage. RBDs work by creating a mapping between a logical block device and a Ceph Storage Cluster. This mapping allows the logical block device to be used as if it were a physical block device, making it possible to use RBDs with any application that can use a physical block device.