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Storage

Last Updated: 2023-01-28

3 types

3 types of storage: block storage, file storage, object storage(blob=binary large object)

The unit of these 3 types:

  • block storage: evenly sized chunks.
  • file storage: a hierarchy of files in folders
  • blob/object storage: immutable objects, e.g. images, audio or other multimedia objects; sometimes binary executable code is stored as a blob.

Example of storage systems

  • Online Transaction Processing Databases (OLTP)
    • Facebook Graph, mission critical, strong consistency, core services
  • Semi-online Light Transaction Processing Databases (SLTP)
    • Facebook Messages and Facebook Time Series
  • Immutable DataStore
    • Photos, videos, etc
  • Analytics DataStore
    • Data Warehouse, Logs storage

Facebook example. This is adapted from this slide

Service Technology Bottlenecks Latency Consistency Durability
Facebook Graph MySQL/TAO Random read IOPS few ms quickly consistent across data centers no data loss
Messages and Time Series HBase and HDFS Write IOPS/storage capacity < 200 ms consistent within a data center no data loss
Photos / Videos Haystack storage capacity < 250 ms immutable no data loss
Data Warehouse Hive / Presto / HDFS storage capacity < 1min not consistent across data centers no silent data loss

The core of a distributed storage system

  • sharding strategy
  • metadata storage

Distributed File Systems

Distributed file systems: GFS, Colossus, Alluxio, CephFS, HDFS

  • Cluster level, fault tolerant, distributed file systems:
    • append only
    • not for structured data(use database instead)
    • not optimized for small files
    • cluster level, not data center level, data destroyed after the cluster turns down
  • HDFS is the open source version of GFS(Google File System)
  • Colossus is the successor of GFS
  • Spanner uses Colossus to store its tablets

Software Defined Storage

  • Ceph: by Red Hat; object store at its core, but support all 3 types (object, block, file). For shorter-term stoarge and more frequent user access.
    • CephFS: a POSIX-compliant network file system
  • Gluster: scalable file storage with object capabilities; also by Red Hat. Should not be used for something transactional, like a database or something that depends on really strict locking.
  • Alluxio: a virtual distributed storage system
  • MinIO: S3 compatible object storage, k8s native.
  • Rook: as a storage orchestrator (can be used with Ceph where Ceph is a storage provider, Rook: Ceph Operator + Discovery)
  • VMware vSAN: creates shared storage for VMs.
  • HDFS: part of Hadoop
  • Netapp