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Discuss Class for Rest of Semester

Chapter 12 Mass-Storage Structure

Magnetic Disks
platters, arms, tracks, sectors, cylinders
transfer rate
positioning time (random-access time) = seek time + rotational latency
head crash
I/O bus -- EIDE, ATA, SATA, USB, FC, SCSI, IEEE 1394 (Firewire)
host controller vs. disk controller

Magnetic Tape

Disk Structure
logical blocks, low-level formatting
constant linear velocity (CLV) vs. constant angular velocity (CAV)
host-attached storage, network-attached storage, storage-area network

Disk scheduling
FCFS
SSTF
SCAN (elevator) vs. LOOK
C-SCAN vs. C-LOOK
Selection/performance depends on number & type of requests and
Selection/performance depends on file-allocation method
SSTF or LOOK reasonable defaults
Disk scheduling in controller vs. OS

Disk Management
Formatting -- low-level (physical) vs. logical formatting
Error-correcting code (ECC) & soft error
Partitioning
Raw Disk
Boot block & bootstrap
E.g. Win 2000 -- master boot record, boot partition, boot sector
Bad blocks -- sector sparing, sector slipping, hard error

Swap-Space Management -- virtual memory uses disk as extension to main memory
Better to overestimate
Location -- normal file system vs. separate partition (often raw partition)

RAID -- redundant array of inexpensive/independent disks
Better performance vs. greater reliability
Mirroring, redundancy
MTTF, MTTR, MTTDL -- calculation, p 469
Independence of failure assumption
Parallelism -- data striping (bit-level vs. block-level)

RAID Levels
0 -- striping blocks, no redundancy
1 -- disk mirroring
2 -- EECs
3 -- bit-interleaved parity
4 -- block-interleaved parity
5 -- block-interleaved distributed parity
6 -- 5 w/ extra redundant information
0+1 & 1+0-- combinations of RAID 0 and RAID 1
Location -- software, host bus-adapter, hardware of storage array, SAN interconnect
Hot spare
CAVEAT -- RAID does not assure data are available

Stable-Storage
Success vs. partial failure vs. total failure

Tertiary-Storage
Removable media
Tapes -- API & locate(); name space problem; jukebox

Economics
Speed -- sustained bandwidth, effective bandwidth (includes access latency)
Reliability -- removable less reliable, optical more reliable
(failure of drive vs. lost data)
Cost -- Disks prices rendering tertiary storage obsolete, disk costs falling faster than memory

Innovator Dilemma -- Clayton Christensen