main memory — dram • secondary storage — disk, network...
TRANSCRIPT
![Page 1: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/1.jpg)
Memory
• Main memory — DRAM
• Secondary storage — disk, network
• Tertiary storage — tape
1
![Page 2: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/2.jpg)
DRAM Prices
2
![Page 3: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/3.jpg)
Disk Prices
3
![Page 4: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/4.jpg)
Tape Prices
4
![Page 5: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/5.jpg)
Storage Choices
• Tape is now cheaper only if you need lots of tape
OSes designed around disk properties, instead
• Disk is still a lot cheaper than DRAM
NAND may change the equation
5
![Page 6: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/6.jpg)
Network-Area Storage (NAS)
e.g., NFS
6
![Page 7: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/7.jpg)
Storage-Area Network (SAN)
7
![Page 8: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/8.jpg)
Backing NAS with Disks
8
![Page 9: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/9.jpg)
Local Disk Partitioning
9
![Page 10: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/10.jpg)
10
![Page 11: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/11.jpg)
• Disk is 3-D • OS sees
1-D array ofblocks
11
![Page 12: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/12.jpg)
• Seek time= time tomove headto cylinder
• Rotational
latency =time to getto the rightsector
12
![Page 13: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/13.jpg)
Disk Scheduling
Suppose that you need to read the following blocks:
98, 183, 37, 122, 14, 124, 65, 67
and the dis heda is currently at block 53
Disk scheduling means picking an order to handlethe current requests
13
![Page 14: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/14.jpg)
FCFS
First come, first served
14
![Page 15: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/15.jpg)
SSTF
Shortest seek time first
15
![Page 16: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/16.jpg)
SCAN
Keep moving in one direction
16
![Page 17: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/17.jpg)
C-SCAN
Always move in one direction
17
![Page 18: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/18.jpg)
C-LOOK
ONly go as far as requests need
18
![Page 19: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/19.jpg)
Choosing an Algorithm
• SSTF is a popular choice
• SCAN and C-SCAN for systems where disk isused heavily
19
![Page 20: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/20.jpg)
RAID
RAID = redundant array of independent disks
• Performance through parallelism
• Reliability through copies
20
![Page 21: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/21.jpg)
RAID
21
![Page 22: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/22.jpg)
RAID 0
Multiple disks ⇒ better preformance
22
![Page 23: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/23.jpg)
RAID 1
Mirrored disks ⇒ better reliability
23
![Page 24: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/24.jpg)
RAID 2
Use parity bits & ECC
• Better reliability
• Fewer disks than RAID 1
24
![Page 25: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/25.jpg)
RAID 3
Single parity bit
• Assumes disk can detect its own bad blocks
• Fewer disks than RAID 2
• Slower writes
25
![Page 26: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/26.jpg)
RAID 4
Single parity bit
• Same space as RAID 3
• Easier to add disks
26
![Page 27: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/27.jpg)
RAID 5
Distribute parity bits
• Same benefits as RAID 4
• Avoids bottleneck of a single parity-bit disk
27
![Page 28: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/28.jpg)
RAID 6
Generalize parity bits to ECC
• Can survive multiple disk failures
• More storage than RAID 5
28
![Page 29: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/29.jpg)
RAID 0+1
29
![Page 30: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/30.jpg)
RAID 1+0
30
![Page 31: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/31.jpg)
Checksums
31
![Page 32: Main memory — DRAM • Secondary storage — disk, network ...mflatt/past-courses/cs5460/lecture14.pdf · • Secondary storage — disk, network • Tertiary storage — tape 1](https://reader034.vdocuments.site/reader034/viewer/2022042909/5f3d62877ce4ac52d904b21a/html5/thumbnails/32.jpg)
Summary
• Compared to main memory, disks are big andslow
• It’s worth complicating the OS to gain I/Operformance
• Keep an eye on SSD developments, which makethis all irrelevant
32