Suggested Exercise 9

1
Suggested Exercise 9

• Sarah Diesburg
• Operating Systems
• CS 3430

2
Hierarchical Name Space

• To access the data content of /pets/cat.jpg
• The system needs to perform the following disk
  I/Os
• 1. Read in the file header for the root directory
  /
• Stored at a fixed location on disk

3
Hierarchical Name Space

• To access the data content of /pets/cat.jpg
• The system needs to perform the following disk
  I/Os
• 2. Read the first data block for the root
  directory
• Lookup the directory entry for pets

pets
4
Hierarchical Name Space

• To access the data content of /pets/cat.jpg
• The system needs to perform the following disk
  I/Os
• 3. Read the file header for pets

pets
pets
5
Hierarchical Name Space

• To access the data content of /pets/cat.jpg
• The system needs to perform the following disk
  I/Os
• 4. Read the first data block for the pet
  directory
• Lookup the directory entry for cat.jpg

pets
pets
cat
6
Hierarchical Name Space

• To access the data content of /pets/cat.jpg
• The system needs to perform the following disk
  I/Os
• 5. Read the file header for cat.jpg

pets
cat
pets
cat
7
Hierarchical Name Space

• To access the data content of /pets/cat.jpg
• The system needs to perform the following disk
  I/Os
• 6. Read the data block for cat.jpg

pets
cat
pets
cat
8
Hierarchical Name Space

• So how many disk I/Os do we need to resolve the
  path?
• Depends what resolving means
• 5 to resolve the path (everything but reading the
  file)
• 6 if resolving includes reading the first file
  data block

9
How would you design your file system differently?

• If you have infinite number of CPUs?
• If you have infinite memory size?
• If you have infinite disk storage?
• If you have infinite network bandwidth?

10
File System Components

• Disk layout
• Naming
• Protection
• Reliability

11
Infinite Number of CPUs

• Some of you forgot to think about disk seek and
  data transfer times
• These are separate from computational power
• Use naming schemes that take a lot of
  computational power
• E.g., relational, contextual, content-based
• Hash data block locations
• Maybe encryption for extra security

12
Infinite Memory Size

• Load (cache) all file to data mappings into
  memory on boot
• Memory-map files to disk

13
Infinite Disk Storage

• Make extra copies for reliability
• Make extra copies for speed
• Contiguous or segment-based allocation
• No longer need to worry about external
  fragmentation

14
Infinite Network Bandwidth

• Automatic remote copy (remote RAID 1?)
• Store metadata locally (accessed more often),
  store data remotely (accessed less often)

15
How would you design a file system

• for only large files?
• for only small files?
• if memory capacity disk capacity

16
For large files

• Multi-level indexed allocation
• Hash allocation change to one block wont
  affect rest

17
For small files

• Indexed allocation
• Small segmented allocation

18
Memory capacity Disk capacity

• Cache all metadata and files as they are being
  used