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Storage Systems: Advanced Topics

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  1. Storage Systems: Advanced Topics Learning Objectives: • To understand limitations of “one file system per partition” model • To understand Logical Volume Management – its motivations and its facilities • To understand how Storage Area Networks extend these features to multiple systems • To relate LVM and SAN to a most modern file system implementation COMP25212

  2. Storage Virtualization File System Code • assumes 1 file system • to 1 disk drive (partition) Stripe/Mirror/RAID changes this Storage Virtualization: break filesystem/drive relationship OS File System Device Drivers COMP25212

  3. Logical Volume Management • Virtual mapping between file system code and physical device • Analogous (but not identical!) to virtual memory addressing • “Volume Group” of all drives in a pool • Storage space in “Volume Group” divided into “Physical Extents” – usually all same size • “Logical Volume” is set of “Physical Extents” COMP25212

  4. Logical Volume Management • Mirror/Stripe/RAID provided within LVM layer • Resize filesystem • “Snapshot” a live filesystem OS File System LVM layer Device Drivers Volume Group COMP25212

  5. e.g. Linux Server • / - mostly read – want fast seeks • swap – read/write – want high bandwidth • /opt – infrequent access • /var – huge, infrequent access • Mirror / • Stripe swap • spare space to /opt and /var COMP25212

  6. LVM Example: Mirror / Stripe swap • Now we can share resources more flexibly and more efficiently – but only on one server /opt /var COMP25212

  7. Storage Area Networking • Implement LVM features in separate storage controller • Connect multiple servers to storage controller • via SCSI, or FibreChannel, or Infiniband, or … (n.b. SAN over Ethernet is conventionally called Networked Attached Storage (NAS) • Now can share disk resources across multiple servers • Rapid migration of disk images COMP25212

  8. Storage Area Network Controller SAN Controller 8 “Blade Servers” COMP25212

  9. SAN Key Features • Functionality • Key element of “system virtualization” • Migrating virtual machines • “De-duping” – share common subsets of file systems (think Virtual Machine images!) • Management: • Manage storage separately from server physical resources • Maximize flexibility of storage provisioning COMP25212

  10. ZFS – Volume Aware File System Marketing claims: • Lost a file? • Run out of space? • Difficult disk upgrade? • Want to grow/shrink? • Data Corruption? Pools of storage COMP25212

  11. ZFS techniques • Lost a file? • Copy-on-write – simple rollback/recovery • Run out of space/Difficult disk upgrade? • Add new storage to live systems • Self-checking, self-healing • Want to grow/shrink? • Data Corruption? • end-to-end sumchecking COMP25212

  12. ZFS Implementation • ZFS Combines File Service and Logical Volume Management • Is this a good idea? Discuss COMP25212