1. Sarah Diesburg Operating Systems CS 3430
Suggested Exercise 7
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 won’t 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