On Sat, Jan 11, 2025 at 3:25 AM Felix E. Klee wrote: > > On Fri, Jan 10, 2025 at 6:37 PM Ryusuke Konishi > <konishi.ryusuke@xxxxxxxxx> wrote: > > Example: > > $ sudo nilfs-clean -S 20/0.1 > > Thank you! That improved things. But there is still a lot of overhead. > It’s 3.0TB in total vs. 2.5TB actually used by files: > > $ sudo nilfs-clean -S 20/0.1 > $ df -h /bigstore/ > Filesystem Size Used Avail Use% Mounted on > /dev/mapper/bigstore 3.5T 3.0T 338G 91% /bigstore > $ du -sh /bigstore/ > 2.5T /bigstore/ > > As mentioned in my original email, initially usage according to `df` was > 3.3TB. So only 0.3TB have been gained. > > > $ sudo lssu -l > > It generates 28 MB of data that starts off like this: > > SEGNUM DATE TIME STAT NBLOCKS NLIVEBLOCKS > 3 2025-01-10 12:19:48 -d-- 2048 2036 ( 99%) > 4 2025-01-10 12:19:48 -d-- 2048 2040 ( 99%) > 5 2025-01-10 12:19:48 -d-- 2048 2036 ( 99%) > 6 2025-01-10 12:19:48 -d-- 2048 2040 ( 99%) > 7 2025-01-10 12:19:48 -d-- 2048 2036 ( 99%) > > I have no idea what to make out of this. The output seems to be after GC, but by default nilfs considers blocks less than an hour old as live (in use), so if you run "lssu -l" again or add the "-p 0" option to set the protection period to 0 seconds, the results may be different. $ sudo lssu -l -p 0 Note that the disk capacity output of the df command includes the reserved space of the file system. By default, NILFS reserves 5% of the disk capacity as a reserved space for GC and normal file system operations (the ratio is the same as ext4). Therefore, the effective capacity of a 3.5TiB disk is about 3.3TiB. In addition to that, NILFS has overhead due to various metadata, the largest of which are DAT for disk address management (1), segment summary for managing segments and logs (2), and B-tree blocks (3). Of these, (3) should be included in the du output capacity, so (1) and (2) are likely to be the main causes. (1) is just over 32 bytes per 4KiB block, which is about 0.78%, and (2) is at most 1.5% depending on usage, so there is a total overhead of just over 2.3%. If the effective capacity is 3.3TiB, the calculated overhead is 0.076TiB, so the upper limit capacity should be around 3.2TiB (theoretically). Other factors may include the 3600 second protection period, and the fact that the NILFS df output is roughly calculated from used segments rather than actual used blocks, so this difference may be affecting it. Regards, Ryusuke Konishi
