IMO, used should definitely include metadata, especially given that we inline small files.
I can convince myself both that this implies that we should roll it into b_avail, and that we should go the other way and only report the actual used number for metadata as well, so I might just plead insanity here. On Mon, Feb 10, 2014 at 12:28 PM, Josef Bacik <jba...@fb.com> wrote: > > > On 02/10/2014 01:24 PM, cwillu wrote: >> >> I concur. >> >> The regular df data used number should be the amount of space required >> to hold a backup of that content (assuming that the backup maintains >> reflinks and compression and so forth). >> >> There's no good answer for available space; the statfs syscall isn't >> rich enough to cover all the bases even in the face of dup metadata >> and single data (i.e., the common case), and a truly conservative >> estimate (report based on the highest-usage raid level in use) would >> report space/2 on that same common case. "Highest-usage data raid >> level in use" is probably the best compromise, with a big warning that >> that many large numbers of small files will not actually fit, posted >> in some mythical place that users look. >> >> I would like to see the information from btrfs fi df and btrfs fi show >> summarized somewhere (ideally as a new btrfs fi df output), as both >> sets of numbers are really necessary, or at least have btrfs fi df >> include the amount of space not allocated to a block group. >> >> Re regular df: are we adding space allocated to a block group (raid1, >> say) but not in actual use in a file as the N/2 space available in the >> block group, or the N space it takes up on disk? This probably >> matters a bit less than it used to, but if it's N/2, that leaves us >> open to "empty filesystem, 100GB free, write a 80GB file and then >> delete it, wtf, only 60GB free now?" reporting issues. >> > > The only case we add the actual allocated chunk space is for metadata, for > data we only add the actual used number. So say say you write 80gb file and > then delete it but during the writing we allocated a 1 gig chunk for > metadata you'll see only 99gb free, make sense? We could (should?) roll > this into the b_avail magic and make "used" really only reflect data usage, > opinions on this? Thanks, > > Josef -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
