Suggested Exercise 9
Sarah Diesburg
Operating Systems
CS 3430
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
/
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
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
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
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
pets
cat
cat
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
pets
cat
cat
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
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?
File System Components
 Disk layout
 Naming
 Protection
 Reliability
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
Infinite Memory Size
 Load (cache) all file to data mappings into
memory on boot
 Memory-map files to disk
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
Infinite Network Bandwidth
 Automatic remote copy (remote RAID 1?)
 Store metadata locally (accessed more
often), store data remotely (accessed less
often)
How would you design a file system
 for only large files?
 for only small files?
 if memory capacity == disk capacity
For large files
 Multi-level indexed allocation
 Hash allocation – change to one block won’t
affect rest
For small files
 Indexed allocation
 Small segmented allocation
Memory capacity = Disk capacity
 Cache all metadata and files as they are
being used