File system Problems

• FS spreads data around disk

  • files are physically separate
  • metadata (inodes) and data separate

• FS performs synchronous writes

  • applications become disk-bound
  • file cache not utilized

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individuals file are laid out sequentially - but not together

metadata - attribute/data/directory entry are separate

5 I/O’s to create a file:

2 access to file attributes

1 access to file data

1 access to directory data

1 access to directory attribute

< 5% of disk BW utilized in FFS

synchronous writes are bad:

performance becomes disk-bound (waiting for disk to finish)

How about “buffered writes on disk”?

Lots of small writes - overhead dominates (SCSI/bus/filesystem/disk/etc)