It is a brief review of secondary storage technologies to find that how we can use it better in our systems.

1. Secondary Storage
A BRIEF REVIEW OF HARD DISK DRIVES AND
STORAGE TECHNOLOGIES

2. Internal Structure
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3. Internal Structure (Cont.)
• Head flies above platters
• Platter are divided into circular tracks and tracks which are
subdivided into sectors. The set of tracks at one arm position make
cylinder.
• Logical blocks, the smallest
unit of transfer (512 bytes)
that maps to the sectors.
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4. Internal Structure (Speed)
• Disk speed has two parts:
•
Transfer Rate, the rate at each data flow between the drive and computer.
•
•
Efficient Transfer Rate
Position Time (Random-Access Time),
•
•
Seek time, the time necessary to move disk arm to the desired cylinder.
Rotational Latency, time necessary for the desired sector to rotate to disk head.
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5. Internal Structure (Head Crash - Connection)
• Head Crash, head may contact the surface
• I/O bus connects Disk Drive to the computer.
EIDE
• ATA, PATA, SATA
• USB
• FC
• SCSI
• FireWire! (Developed by Apple, IEEE 1934 standard) (400 Mbps)
•
• A disk controller is built into each disk drive that has a cache ...
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7. Magnetic Tapes
• Early secondary storages with very slow access time (1000 times
slower than HDD)
• Can be used for back up or non-frequently used data.
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8. Disk Attachment
• Host-Attachment Storage (via I/O) common for small systems.
• Network-Attach Storage, remote host in a distributed file system
•
•
Remote-procedure call interface (NFS for UNIX, CIFS for windows)
NAS is implemented as a RAID (redundant array of independent disks) array
with software that implements RPC interface.
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9. NAS
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10. Server
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11. Storage Area Network
• Drawback in NAS: Storage I/O operations consume Bandwith
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12. SAN
• Oracle
• Google
• Hp
• …
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13. RAID
• Disks get smaller and cheaper
• Redundant Arrays of Independent (not completely) Disks
• Inexpensive -> Independent
• Increasing read and write rate (Parallel) - increase the throughput
(load balancing) / reduce response time of large accesses
• Increasing Reliability (Redundant) – Mirroring
• RAID levels (Redundancy to Striping)
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14. RAID Levels – 0
• Nothing
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15. RAID Levels – 1
• Mirroring
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16. RAID Levels – 2
• Parity bits - ECC
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17. RAID Levels – 3
• Parity bits
• Less disks
• Much Speed
• fewer I/O
• Dedicated Parity Hardware
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18. RAID Levels – 4
• Like 3 but blocks in each disk
• Higher level of I/O rate
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19. RAID Levels – 5
• Spreading the parity blocks
• Safer - Most Common
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20. RAID Levels – 6
• Like 5, Parity + Reed Solomon ECC Code
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21. RAID Levels – 0+1 , 1+0
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22. Choosing a RAID Level
• Continues supply of data is needed
•
Rebuilding is easiest in RAID level 1
• Level 0 for high performance where data loss is not so important
• Level 1+0 and 0+1 for both Performance and reliability (ex. Small
Databases)
• Level 5 can be used instead of 1
• Level 6 is not supported commonly, but it should be more reliable
that level 5
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23. • How many disks should be in a given
RAID set?
•
More disks, More Data-Transfer
Rate, More Expensive
• How many bits should be protected
by each parity bit?
WHAT SHOULD WE
THINK ABOUT?
•
Less bits each parity, More Chance to
Modify the Failure, More Overhead
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24. SSD VS. HDD
Solid State Drive
Hard Disk Drive
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