Cpr E 545 Presentation 1

Data Protection onMagnetic Hard DriveDevice ArraysRuss Graves

RAID Advantages• Good for speed & reliability underoptimum conditions• Total (fail-stop) drive failures are easy todeal with

RAID Disadvantages• Handling of corrupted sectors can causeambiguous data• Software/system crashes can leave uncleanstates• Multiple faults can fail the entire array• Correlated drive failures are a problem

RAID Research• Linux RAID levels with corrupted data• Ability of arrays to recover from multipledisks with errors

Filesystems• Assume perfect block device• Many have superblock backups• No production local FS with per-fileredundancy

FilesystemConsiderations• Speed - Read, write, modify, failureperformance• Size of files protected

Head Crash

Hard Drive Failures• NOT fail stop as assumed by many systems• Corrupted or unreadable sectors• SMART does not help• Infrequently accessed areas

Research• Analysis of available drive scans• Drive monitoring systems• Online RAM testing• Safe RW testing

References• RAID: High-Performance, ReliableSecondary Storage (Peter Chen, ACMComputing Surveys, Vol 26, No 2, 1994)• Failure Trends in a Large Disk DrovePopulation (Pinheiro, Weber, Barroso, FAST‘07)

Questions?