On 9/16/13 9:44 AM, Nicolas Michel wrote: > 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?) # dumpe2fs /dev/$YOUR_DEVICE | grep Journal dumpe2fs 1.41.12 (17-May-2010) Journal inode: 8 Journal backup: inode blocks Journal features: journal_incompat_revoke Journal size: 128M Journal length: 32768 But you also need to take into account inode tables, inode allocation bitmaps, block allocation bitmaps ... -Eric > 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 >>> >>> >> > > > _______________________________________________ Ext3-users mailing list Ext3-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/ext3-users
