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Ceph

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• Explain what is Ceph
  Answer

  Ceph is an Open-Source Distributed Storage System designed to provide excellent performance, reliability, and scalability. It's often used in cloud computing environments and Data Centers.

• True or False? Ceph favor consistency and correctness over performances
  Answer

  True

• Which services or types of storage Ceph supports?
  Answer

  • Object (RGW)
  • Block (RBD)
  • File (CephFS)
• What is RADOS?
  Answer

  • Reliable Autonomic Distributed Object Storage
  • Provides low-level data object storage service
  • Strong Consistency
  • Simplifies design and implementation of higher layers (block, file, object)
• Describe RADOS software components
  Answer

  • Monitor
    • Central authority for authentication, data placement, policy
    • Coordination point for all other cluster components
    • Protect critical cluster state with Paxos
  • Manager
    • Aggregates real-time metrics (throughput, disk usage, etc.)
    • Host for pluggable management functions
    • 1 active, 1+ standby per cluster
  • OSD (Object Storage Daemon)
    • Stores data on an HDD or SSD
    • Services client IO requests
• What is the workflow of retrieving data from Ceph?
  Answer

  The work flow is as follows:

  1. The client sends a request to the ceph cluster to retrieve data:

  Client could be any of the following

  • Ceph Block Device
  • Ceph Object Gateway
  • Any third party ceph client

  2. The client retrieves the latest cluster map from the Ceph Monitor
  3. The client uses the CRUSH algorithm to map the object to a placement group. The placement group is then assigned to a OSD.
  4. Once the placement group and the OSD Daemon are determined, the client can retrieve the data from the appropriate OSD
• What is the workflow of writing data to Ceph?
  Answer

  The work flow is as follows:

  1. The client sends a request to the ceph cluster to retrieve data
  2. The client retrieves the latest cluster map from the Ceph Monitor
  3. The client uses the CRUSH algorithm to map the object to a placement group. The placement group is then assigned to a Ceph OSD Daemon dynamically.
  4. The client sends the data to the primary OSD of the determined placement group. If the data is stored in an erasure-coded pool, the primary OSD is responsible for encoding the object into data chunks and coding chunks, and distributing them to the other OSDs.
• What are "Placement Groups"?

  🚧 Answer not written yet.

• Describe in the detail the following: Objects -> Pool -> Placement Groups -> OSDs

  🚧 Answer not written yet.

• What is OMAP?

  🚧 Answer not written yet.

• What is a metadata server? How it works?

  🚧 Answer not written yet.