Thanks for you help. I also tried adding some other informations as you suggest: I can also take into account: - "Reserved block count: XXXXXXX" from tune2fs that gives me the number of blocks reserved for root - Reserved GDT blocks: XXX But I didn't thought about the FS journal. How can I gather information about it? (it's size and any other information?) 2013/9/16 Eric Sandeen <sandeen@xxxxxxxxxx>: > On 9/16/13 5:16 AM, Nicolas Michel wrote: >> Hello guys, >> >> I have some difficulties to understand what really are the numbers >> behing "df" and tune2fs. You'll find the output of tune2fs and df >> below, on which my maths are based. >> >> Here are my maths: >> >> A tune2fs on an ext3 FS tell me the FS size is 3284992 block large. It >> also tell me that the size of one block is 4096 (bytes if I'm not >> wrong?). So my maths tell me that the disk is 3284992 * 4096 = >> 13455327232 bytes or 13455327232 / 1024 /1024 /1024 = 12.53 GB. >> >> A df --block-size=1 on the same FS tell me the disk is 13243846656 >> which is 211480576 bytes smaller than what tune2fs tell me. > > By default, df on extN assumes that metadata used by the filesystem > was never available for your use and is not part of the filesystem > space. > > Documentation/filesystems/ext3.txt says: > > bsddf (*) Make 'df' act like BSD. > minixdf Make 'df' act like Minix. > > which is pretty unhelpful I suppose. ;) > > The mount man page is a little more helpful: > > bsddf|minixdf > Set the behaviour for the statfs system call. The minixdf > behaviour is to return in the f_blocks field the total number > of blocks of the filesystem, while the bsddf behaviour (which > is the default) is to subtract the overhead blocks used by the > ext2 filesystem and not available for file storage. > > You're seeing the latter behavior. if you mount with -o minixdf you should > see what you expect. (Too bad there's no "linuxdf?") :) > >> In gigabytes, it means: >> * for df, the disk is 12.33 GB >> * for tune2fs, the disk is 12.53 GB >> >> I thought that maybe df is only taking into account the real blocks >> available for users. So I tried to remove the reserved blocks and the >> GDT blocks: >> (3284992 - 164249 - 801) * 4096 = 12779282432 >> or in GB : 12779282432 / 1024 / 1024 / 1024 = 11.90 Gb ... > > you're on the right track, but you forgot the journal space, all the > preallocated inode table blocks, etc. > > -Eric > >> My last thought was that "Reserved block" in tune2fs was not only the >> reserved blocks for root (which is 5% per default on my system) but >> take into account all other reserved blocks fo the fs internal usage. >> So: >> (3284992 - 164249) * 4096 = 12782563328 >> In GB : 11.90 Gb (the difference is not significative with a precision of 2. >> >> So I'm lost ... >> >> Is someone have an explanation? I would really really be grateful. >> Nicolas >> >> ------------------------------ >> --------- >> >> Here is the output of df and tune2fs : >> >> $ tune2fs -l /dev/mapper/datavg-datalogslv >> tune2fs 1.41.9 (22-Aug-2009) >> Filesystem volume name: <none> >> Last mounted on: <not available> >> Filesystem UUID: 4e5bea3e-3e61-4fc8-9676-e5177522911c >> Filesystem magic number: 0xEF53 >> Filesystem revision #: 1 (dynamic) >> Filesystem features: has_journal ext_attr resize_inode dir_index >> filetype needs_recovery sparse_super large_file >> Filesystem flags: unsigned_directory_hash >> Default mount options: (none) >> Filesystem state: clean >> Errors behavior: Continue >> Filesystem OS type: Linux >> Inode count: 822544 >> Block count: 3284992 >> Reserved block count: 164249 >> Free blocks: 3109325 >> Free inodes: 822348 >> First block: 0 >> Block size: 4096 >> Fragment size: 4096 >> Reserved GDT blocks: 801 >> Blocks per group: 32768 >> Fragments per group: 32768 >> Inodes per group: 8144 >> Inode blocks per group: 509 >> Filesystem created: Wed Aug 28 08:30:10 2013 >> Last mount time: Wed Sep 11 17:16:56 2013 >> Last write time: Thu Sep 12 09:38:02 2013 >> Mount count: 18 >> Maximum mount count: 27 >> Last checked: Wed Aug 28 08:30:10 2013 >> Check interval: 15552000 (6 months) >> Next check after: Mon Feb 24 07:30:10 2014 >> Reserved blocks uid: 0 (user root) >> Reserved blocks gid: 0 (group root) >> First inode: 11 >> Inode size: 256 >> Required extra isize: 28 >> Desired extra isize: 28 >> Journal inode: 8 >> Default directory hash: half_md4 >> Directory Hash Seed: ad2251a9-ac33-4e5e-b933-af49cb4f2bb3 >> Journal backup: inode blocks >> >> $ df --block-size=1 /dev/mapper/datavg-datalogslv >> Filesystem 1B-blocks Used Available Use% Mounted on >> /dev/mapper/datavg-datalogslv 13243846656 563843072 12007239680 5% /logs >> >> > -- Nicolas MICHEL _______________________________________________ Ext3-users mailing list Ext3-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/ext3-users
