OK. Thanks for the journal information. I thought tune2fs -l and dumpe2fs were the same. In reality it's almost the same but not entirely ^^ I hear you about all the internal mecanisms that make the FS working or give it some features, and I do understand that it takes some place on the disk. However what I don't understand is why the number given in the "available column" is called "available" if it's not really the case and we have to remove some other thousand/million of bytes for some internal mecanisms. In other words I don't understand why the "used" percentage given by df does not reflects the values given by itself in the other columns. I can live with it but I really would like to understand why things are what they are. Is there an historic reason? Or maybe a technical reason that makes thoses numbers some added values? The least would be to have the df algorithms documented somewhere? A document that explains intentions and how the values are obtained. The same for tune2fs and dumpe2fs (what really means the given numbers?) 2013/9/16 Eric Sandeen <sandeen@xxxxxxxxxx>: > 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 >>>> >>>> >>> >> >> >> > -- Nicolas MICHEL _______________________________________________ Ext3-users mailing list Ext3-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/ext3-users
