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Suppose a UNIX file system has some constraints--say, 2 KB blocks and 8B disk addresses. What is the maximum file size if inodes contain 13 direct entries, and one single, double, and triple indirect entry each?

solvingPuzzles
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3 Answers3

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This explains it for you:

http://www.cis.temple.edu/~ingargio/cis307/readings/stable.html

"The maximum size of a file will be 8KB*(10 + 2**10 + 2**20 + 2**30), that is more than 8TB."

Swap 8KB for your 2KB, and adjust the entries for the smaller block size.

2KB*(10 + 2**8 + 2**16 + 2**24)

It's not clear to me from your question if the 13 entries include the singles, doubles and triples, or if they are separate, but that should be easy to adjust -- just change the 10 in the expression to a 13.

I think I've adjusted all the math correctly... double check it =| Hope this isn't homework I did for you ;)

WhirlWind
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    Sorry to bother you with a question 7 years later on this, but what do the two variables mean inside the equation? `2**10` or `2**20` - why 2 and why 10 or 20 for each? – NateH06 Apr 01 '17 at 19:49
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    @NateH06 `2**10` means `2^10`, and I think those numbers are as follows: 10 is for 10 direct entries, `2^10 = 1024`, which is 1024^1. `2^20 = 1024^2 and 2^30 = 1024 ^ 3` each index block contains 1024 pointers, so it makes sense. Result is `1,000,000,000 KB = 8.59833 TB` – MuhsinFatih Nov 28 '18 at 16:49
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How many pointers in 1 block? 

     each block is 2kb = 2^11
     1 disk address is 8b = 2^3
     So, in 1 block there are 2^11/2^3 = 2^8 pointers"

How many pointers in the file system? 

     for 13 direct entries = (2^8)*13 = 3328
     for single  = (2^8)^2 = 2^16
     for double = (2^8)^3 = 2^24
     for triple = (2^8)^4 = 2^32
     total pointer is :3328 + 2^16 + 2^24 + 2^32"

Therefore the size of the file system is: 

size of the disk is  : total of pointer*size of the pointer , which is around 34 GB "
user3035698
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We hv a shortcut that can be used for competitive exams, given as :

Max file size possible = [ block size/pointer size]^3 * block size
V-rund Puro-hit
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Surbhi Kaushik
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