M4rtinK · April 25, 2017 13:43
diff --git a/gistfile1.txt b/gistfile1.txt
 [QUOTE=RussianNeuroMancer;n947934]Btrfs used in Jolla phones and tablets.[/QUOTE]
 That's actually no longer true - it was used in the first Sailfish OS device (the "Jolla 1" smartphone), but there were serious issues with it and new devices (Jolla Tablet, Jolla C, Intex Aquafish, community ports, etc.) all run EXT4 on top of LVM.

 AFAIK, these were the reasons why Jolla dropped btrfs:
 - metadata block exhaustion resulting in filesystem write operations failing at random
  - The Jolla 1 internal storage was about 16 GB big. Btrfs allocates data and metadata block on demand, starting with one data and one metadat block being allocated. Then it would often happen that the remaining free space will be all allocated to data blocks (as the users adds big files to the device, records video, etc.). Things would still work for a while, until the single metadata block gets full and there is no unallocated space for a new metadata block. Result: filesystem operations failing at random, Oops! :P
 - Bogus free space reporting - due to the issue above (there is enough space for data, just not for the metadata associated with the new files) and data "preserved" by snapshots free space reporting was very unreliable.
 - Btrfs balance issues.
  - ballancing is run periodically on Jolla 1 in an attempt to make thing a bit more bearable (eq. dealocate some data blocks so that new metadata blocks can be written)
  - this still often fails to free any data block even when there are multiple GB of free space reported by btrfs
  - the btrfs balancing tool sometimes crashes or runs indefinitely
 - Btrfs snapshots have been used for factory reset, which has not turned out as a good idea.
  - the Jolla 1 originally shipped at the end of 2013 and the factory reset snapshot dates from that time
  - any user who performs a factory reset will have to perform multiple consecutive upgrades to get to the 2017 "patch level"
  - there is no robust way to update the factory reset btrfs snapshot to a more recent firmware over network on all devices
  - all storage is allocated to btrfs, so it's not even possible to drop the fs, recreate it and fill it from some recovery partition
  - this has been solved on newer devices by adding a recovery partition that holds squashfs recovery images of the rootfs and home folder; facotry reset just drops the primary storage (ext4 on LVM), recreates it and fill it from the squashfs images; the squashfs recovery images on a separate partition can be easily updated as needed
 - Btrfs also does not work particularly well with the ancient Android kernels Sailfish OS has to use in order to reuse the Android hardware adaptation.
	[QUOTE=RussianNeuroMancer;n947934]Btrfs used in Jolla phones and tablets.[/QUOTE]
	That's actually no longer true - it was used in the first Sailfish OS device (the "Jolla 1" smartphone), but there were serious issues with it and new devices (Jolla Tablet, Jolla C, Intex Aquafish, community ports, etc.) all run EXT4 on top of LVM.

	AFAIK, these were the reasons why Jolla dropped btrfs:
	- metadata block exhaustion resulting in filesystem write operations failing at random
	- The Jolla 1 internal storage was about 16 GB big. Btrfs allocates data and metadata block on demand, starting with one data and one metadat block being allocated. Then it would often happen that the remaining free space will be all allocated to data blocks (as the users adds big files to the device, records video, etc.). Things would still work for a while, until the single metadata block gets full and there is no unallocated space for a new metadata block. Result: filesystem operations failing at random, Oops! :P
	- Bogus free space reporting - due to the issue above (there is enough space for data, just not for the metadata associated with the new files) and data "preserved" by snapshots free space reporting was very unreliable.
	- Btrfs balance issues.
	- ballancing is run periodically on Jolla 1 in an attempt to make thing a bit more bearable (eq. dealocate some data blocks so that new metadata blocks can be written)
	- this still often fails to free any data block even when there are multiple GB of free space reported by btrfs
	- the btrfs balancing tool sometimes crashes or runs indefinitely
	- Btrfs snapshots have been used for factory reset, which has not turned out as a good idea.
	- the Jolla 1 originally shipped at the end of 2013 and the factory reset snapshot dates from that time
	- any user who performs a factory reset will have to perform multiple consecutive upgrades to get to the 2017 "patch level"
	- there is no robust way to update the factory reset btrfs snapshot to a more recent firmware over network on all devices
	- all storage is allocated to btrfs, so it's not even possible to drop the fs, recreate it and fill it from some recovery partition
	- this has been solved on newer devices by adding a recovery partition that holds squashfs recovery images of the rootfs and home folder; facotry reset just drops the primary storage (ext4 on LVM), recreates it and fill it from the squashfs images; the squashfs recovery images on a separate partition can be easily updated as needed
	- Btrfs also does not work particularly well with the ancient Android kernels Sailfish OS has to use in order to reuse the Android hardware adaptation.
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