[DataBase] Storage

Storage Hierarchy

cache : in process L cache
main memory : DRAM
flash memory : Flash
magnetic disk : distk : HDD
optical disk (deprecated)
magnetic tapes (deprecated)

primary storage : cache, main memory
secondary storage : on-line storage, flash memory, magnetic disk
tertiary storage : off-line storage, magnetic tape, optical storage

Storage Interfaces

Direct Connected:

• SATA v3 : 6gbit/sec
• SAS v3 : 12gbit/sec
• NVMe : 24gbit/sec

SAN : Storage Area Networks
NAS : Network Attached Storage

Performance Measures

Access time

• Seek time
• Rotational latency

Data-transfer rate
Disk block
Sequential access pattern
Random access pattern
I/O operations per second (IOPS)
Mean time to failure (MTTF)

Flash Storage

inplace update -> HDD only
copy on write -> NAND Flash
-> FTL (Flash Transition Layer)

RAID

RAID : Redundant Arrays of Independent Disks

• high capacity and high speed
• high reliability

Redundancy
Mirroring(or shadowing)
Striping (bit or block level)

RAID Levels

• RAID 0 : Block Striping

• RAID 1 : Disk Mirroring

• RAID 2 : Bit Interleaving + hamming

• RAID 3 : Bit Interleaving + Parity

• RAID 4 : Block Interleaving + Parity → Parity Disk 병목

• RAID 5 : Block Interleaving + Parity block distbute

• RAID 6 : 2Parity block

• RAID 10 (1 + 0) / RAID 01 (0 + 1) :

• RAID 5 + Hotspare :