Storage  ^sandbox 

Types

Remote vs Local

Media

HDD

SSD

RAID

• What is a “RAID”? Redundant Array of Independent Disks

• What problem does it solve?

• Problems with RAID?

Common Types of RAID

# Minimum number of drives required to create this RAID array ## Number of drives that can fail without data loss

1. RAID 0

• atleast 2 drives
• typically 2 hard drives of equal capacity
• block level striping, no mirroring, no parity
• doubles write speed by writing to 2 drives alternatively
• any failed drive can cause data loss

1. RAID 1

• atleast 2 drives
• mirrored 2 hard drives of equal capacity
• mirroring, but no striping, no parity
• either drive can fail without data loss
• write performance hit due to writing to 2 hard disks, so not good for high performance writes
• read performance similar to raid 0, data can be read from any drive

1. RAID 5

• atleast 3 drives, typically 5
• block level striping, distributed parity
• provides higher capacity than 1, and better redundancy than 0
• array rebuild needs all data to be read, and can cause other drive failures
• 1 drive can fail without data loss

1. RAID 6

• atleast 4 drives, typically 5
• similar to 5, but 2 drives are dedicated for redundancy
• block level striping, double distributed parity
• 2 drives can fail without data loss
• performance hit until a failed drive is replaced. why?
• Software RAID - ZFS (RAID-Z3)

1. RAID 10

• combination of 1 and 0, typically 4 hard drives
• striped set of mirrored hard drives
• benefits of both - redundancy and performace
• twice the cost

Questions

1. What is the definition of storage? Is cache a storage? Is file storage? Why or why not?
2. What is “stripe” re: RAID?
3. What are “parity bits”?
   • Simple form of error detecting code
   • Even (total 1 bits are even) or Odd (total 1 bits are odd)
   • Calculate parity for 1001, even = 1, odd = 0
   • RAIDs recreate data using XOR gate
4. What is a “block”?