1. Storage Technologies Grand Plan: 1.Review/revision, Disks, Filesystems, Limitations and Solutions 2.RAID – build server filestore from PC parts 3.Logical Volume Management, Storage Area Networking, Next-Generation Filesystems (Google, Sun) COMP25212 1 Feb 2013

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 2 Feb 2013

3. Review – Disk Storage Capacity? Power Consumption? Rotation Speed? Seek? Time? Search? Time? Transfer? Rate? Interface type? Max bandwidth? Price? COMP25212 3 Feb 2013

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 4 Feb 2013

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 5 Feb 2013

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 6 Feb 2013

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 7 Feb 2013

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 8 Feb 2013

9. Disk Striping (increases transfer rate) (increases capacity) (decreases reliability) COMP25212 9 File System Unit 0 File System Unit 1 File System Unit 2 File System Unit 3 Feb 2013

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 10 Feb 2013

11. Is There A Better Way? Yes, but… see next lecture! COMP25212 11 Feb 2013