Optimizing Linux filesystems for cheap flash drives

Posted Feb 20, 2011 9:33 UTC (Sun) by alonz (subscriber, #815)
Parent article: Optimizing Linux with cheap flash drives

Is it possible to hack a special “cheap flash mode” into filesystems such as ext3/ext4/btrfs?

Such a mode could e.g. move the log + inode table + allocation bitmaps etc. to the "FAT" segment (either breaking the info apart from the block groups or maybe even using a single block group for the entire device). Plus it could set the block size to the expected FAT cluster size (after all, these filesystems do know how to use block sizes != page size). Possibly other optimizations can be applied.

Optimizing Linux filesystems for cheap flash drives

Posted Feb 20, 2011 13:47 UTC (Sun) by nix (subscriber, #2304) [Link] (4 responses)

That sounds like a good idea, as many of the rationales for positioning most of these things in the middle of the disk is to reduce seek time, which hardly matters on an SSD.

One downside, though: I suspect the FAT segment is (much) too small.

Optimizing Linux filesystems for cheap flash drives

Posted Feb 21, 2011 13:15 UTC (Mon) by mchazaux (guest, #64024) [Link] (3 responses)

Then do the opposite : add UID, GID, permissions and such to a FAT-like filesystem ;-)

Optimizing Linux filesystems for cheap flash drives

Posted Feb 21, 2011 15:21 UTC (Mon) by giggls (subscriber, #48434) [Link] (2 responses)

One apon a time there has been the UMSDOS filesystem which did exactly this. I'm unaware if this is still available in current kernels though.

Optimizing Linux filesystems for cheap flash drives

Posted Feb 21, 2011 19:36 UTC (Mon) by nix (subscriber, #2304) [Link]

No, it was removed some years ago.

Optimizing Linux filesystems for cheap flash drives

Posted Feb 21, 2011 19:37 UTC (Mon) by arnd (subscriber, #8866) [Link]

It's not, see the discussion about. I think we can do much better than FAT as well, even given the characteristics of the current drives. Ted Ts'o has some ideas for ext4, and my understanding of btrfs is that it does not rely on a specific block allocation at all, so that could be an excellent target as well.

Starting out a completely new file system designed only for SD cards would of course make it possible to get the best result, but that would also be an enormous amount of work.