1 / 6

Disk Access

Disk Access. Seek Algorithms. FCFS SSTF SCAN - ssd in preferred direction CSCAN - outer to inner, ssd, jump to outer FSCAN - scan for only those at start of scan nSCAN - only first n requests LOOK - lookahead & change direction C-LOOK - outer to inner & jump. Rotation Algorithms.

coreym
Télécharger la présentation

Disk Access

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Disk Access

  2. Seek Algorithms • FCFS • SSTF • SCAN - ssd in preferred direction • CSCAN - outer to inner, ssd, jump to outer • FSCAN - scan for only those at start of scan • nSCAN - only first n requests • LOOK - lookahead & change direction • C-LOOK - outer to inner & jump

  3. Rotation Algorithms • SLTF – Shortest Latency Time First • latency, by sector position • SPTF - Shortest Positioning Time First • Time to position the access-head • SATF – Shortest Access Time First • close coupling of CPU and disk • processor knows rotational position of the disk at any time

  4. Other considerations • Cache • Fragmentation • Partitioning • Compression • Record blocking • Hot-spot detection (speeds up access)

  5. problems • Write-through • Coherency is high • Lazy-write • Low coherency

  6. RAID • 0 - striping - no Fault Tolerance • 1 - mirroring (see my patent) • 2 - bit-striping with Hamming parity stripes • 3 - like 2 but XOR ECC stripes • 4 - large block stripes + XOR ECC stripes • 5 - like 4 but parity with data • 0+1 - 2 striped disks + 2 mirrors • 10 - mirrored disks + a striped pair

More Related