CODEWITHSUNDEEP
filesystemsexfat
jb2019
jb2019

Reputation: 111

exFAT cluster allocation strategy

I am attempting to create an exFAT file system implementation for an embedded processor. I have a question about the cluster allocation of a file.

Suppose I have created a file and then written some data to the file. Lets say that the file has used 10 clusters and they are continuous on disk. As far as I understand it, exFAT has a way to mark the file as continuous in the file's directory entry.

Lets say I create more files and write data to them. Then I go back to my first file and want to write more data to the file. But now there are no free clusters at the end of the file as other files occupy them. I guess it must be possible to add more space to the file, but how is this recorded in exFAT? The original file was continuous but now it isnt. The FAT table wouldnt have been updated because of that. Does the FAT table now have to be re-written because the file is fragmented? Thanks

Upvotes: 1

Views: 278

Answers (1)

jb2019
jb2019

Reputation: 111

I did an experiment using a USB pen and a disk utility. It turns out that if you write more data to the file and it becomes fragmented, then the continuous cluster flag gets cleared in the dir entry. Then the FAT table needs to be created to indicate where the clusters for the file are located.

Upvotes: 0

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