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Storage Technologies

Storage Technologies. Grand Plan: Review/revision, Disks, Filesystems, Limitations and Solutions RAID – build server filestore from PC parts Logical Volume Management, Storage Area Networking, Next-Generation Filesystems (Google, Sun). Storage Technologies. Today’s Learning Objectives:

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Storage Technologies

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  1. Storage Technologies Grand Plan: • Review/revision, Disks, Filesystems, Limitations and Solutions • RAID – build server filestore from PC parts • Logical Volume Management,Storage Area Networking,Next-Generation Filesystems (Google, Sun) COMP25212

  2. Storage Technologies Today’s Learning Objectives: • Renew acquaintance with disk and file system characteristics • Describe operational limitations of conventional disk usage • Describe how multiple disks, mirroring and striping overcome these difficulties • Appreciate the complexity of these multiple schemes COMP25212

  3. Review – Disk Storage • Capacity? • Power Consumption? • Rotation Speed? • Seek? Time? • Search? Time? • Transfer? Rate? • Interface type? Max bandwidth? • Price? COMP25212

  4. Review – File Systems Naming Service: • Files, Directories, Links Storage Service: • “Vector of Bytes”, owners, permissions, existence control Data and Metadata Space Allocation (file and free-space): • Contiguous, Linked (FAT), Indexed Recovery – chkdsk, fsck COMP25212

  5. Problems With Disks • They are (were?) too small • They sometimes fail • They are too slow • They are in the wrong place • (think system virtualization) COMP25212

  6. Disks Too Small? • Use multiple disks • How should they be named? • F:/one/two, G:/three/four • /Volumes/first, /Volumes/second • /var/huge-file-store??? Cue: Rawsthorne’s story about a 2.4Tb file COMP25212

  7. Disks Too Unreliable? Failure modes: total, partial Use two (or more…) – “Mirroring” • Write to both, read from either • If one fails, carry on using other • Recreate copy (slowly…) Refinement: read from “nearest” – accelerate reads COMP25212

  8. Disks Too Slow? Slow because of: • Transfer rate? • Search time? • Seek time? To minimise seek time, maximize data available with no seek “stripe” file system across multiple disks COMP25212

  9. Disk Striping File System Unit 0 • (increases transfer rate) • (increases capacity) • (decreases reliability) File System Unit 1 File System Unit 2 File System Unit 3 COMP25212

  10. Problems With Disks They are (were?) too small • Fixed (multiple disks), fixed (striping) They sometimes fail • Fixed (mirroring), worsened (multiple/striping) They are too slow • Fixed (mirroring/striping) They are in the wrong place (think system virtualization) COMP25212

  11. Is There A Better Way? • Yes, but… see next lecture! COMP25212

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