10.08.2018 12:33, Tomasz Pala пишет: > >> For 4 disk with 1T free space each, if you're using RAID5 for data, then >> you can write 3T data. >> But if you're also using RAID10 for metadata, and you're using default >> inline, we can use small files to fill the free space, resulting 2T >> available space. >> >> So in this case how would you calculate the free space? 3T or 2T or >> anything between them? > > The answear is pretty simple: 3T. Rationale: > - this is the space I do can put in a single data stream, > - people are aware that there is metadata overhead with any object; > after all, metadata are also data, > - while filling the fs with small files the free space available would > self-adjust after every single file put, so after uploading 1T of such > files the df should report 1.5T free. There would be nothing weird(er > that now) that 1T of data has actually eaten 1.5T of storage. > > No crystal ball calculations, just KISS; since one _can_ put 3T file > (non sparse, uncompressible, bulk written) on a filesystem, the free space is 3T. > As far as I can tell, that is exactly what "df" reports now. "btrfs fi us" will tell you both max (reported by "df") and worst case min.
