Disk Subsystems

 RAID 0 - Stripe or Concatenation

• Comes in two forms
• Concatenated Disks - size can vary, 1st or last disk tends to be hot.
• Interleaved Disks - by chunk size, typically requires disk/partitions to be same size, or space is wasted.
• Greatest through put
• most sensitive to failure, if a disk is .999 reliable, 4 disk are .999^4 = .996
• load spread across all disks
• Best performance when each disk is on a different channel.
• Worst when all on same.
• Compromise - Alternate between channels

RAID 1 - Mirror / Shadow set

Normally two or more disks that are an exact copy of each other.

Best read performance

Good write preformance

Not much worse than a write to a single disk, does double data transfered, disks on different channels makes a difference.

Fanciers systems allow for removal (split/cleave) of mirror for backup.