Thanks Eric. >> I have an observation on EXT4 filesystem. I created filesystem of size >> 1TB, 4TB, and 7TB and then checked the output of df command. > > Telling us which version of e2fsprogs and which kernel would be helpful, > but: its 1.41.12. > It reserves blocks for the superuser (5% by default) and also uses a lot > of blocks up-front for filesytem metadata - inode tables, block bitmaps, > and the like. I also thinks so. But with this assumption, the number of 1KB blocks used should increase as per filesystem size increase. No? > > But what you are seeing here is this: > > It also defaults to "bsd df" which does not count filesystem > metadata when telling you about the number of blocks used. So in theory, > a freshly made fs should actually tell you 0 blocks used, I think. Agree if "bsd df" assumes so. > Looking at the dumpe2fs output for the 4t file, I see: > > # dumpe2fs -h 4tfile-ext4 | grep -i block > dumpe2fs 1.41.12 (17-May-2010) > Block count: 1073741824 > Reserved block count: 53687091 > Free blocks: 1056843748 > ... > > and 1073741824-1056843748 is 16898076 4k blocks, or 67592304 1k blocks > actually used. > > If we ask for "minix df" by mounting with -o minixdf which is true blocks used, we get: > > # df 4t-ext4/ > Filesystem 1K-blocks Used Available Use% Mounted on > /mnt/test2/mkfs-test/4tfile-ext4 > 4294967296 67592304 4012626628 2% /mnt/test2/mkfs-test/4t-ext4 > > I'd say this appears to be a slight inaccuracy in ext4_statfs, coupled with > the strangeness of the "bsd df" reporting. It is apparently miscalculating > the filesystem metadata "overhead." In your example, dumpe2fs and minix df both are reporting same value, isn't it? I am still not able to understand why increasing the filesystem size decreases used 1K block count :( Am I missing some basic things here? Sorry if i am not able to catch your point :( Regards, Adil On Thu, Feb 7, 2013 at 10:19 PM, Eric Sandeen <sandeen@xxxxxxxxxx> wrote: > On 2/7/13 12:39 AM, Adil Mujeeb wrote: >> Hi, >> >> I have an observation on EXT4 filesystem. I created filesystem of size >> 1TB, 4TB, and 7TB and then checked the output of df command. > > Telling us which version of e2fsprogs and which kernel would be helpful, > but: > >> df command showed the number of 1KB blocks used. The result was: >> 1TB: 204056 >> 4TB: 198680 >> 7TB: 181784 > > extN makes df complicated in several ways. > > It reserves blocks for the superuser (5% by default) and also uses a lot > of blocks up-front for filesytem metadata - inode tables, block bitmaps, > and the like. > > But what you are seeing here is this: > > It also defaults to "bsd df" which does not count filesystem > metadata when telling you about the number of blocks used. So in theory, > a freshly made fs should actually tell you 0 blocks used, I think. > > Looking at the dumpe2fs output for the 4t file, I see: > > # dumpe2fs -h 4tfile-ext4 | grep -i block > dumpe2fs 1.41.12 (17-May-2010) > Block count: 1073741824 > Reserved block count: 53687091 > Free blocks: 1056843748 > ... > > and 1073741824-1056843748 is 16898076 4k blocks, or 67592304 1k blocks > actually used. > > If we ask for "minix df" by mounting with -o minixdf which is true blocks used, we get: > > # df 4t-ext4/ > Filesystem 1K-blocks Used Available Use% Mounted on > /mnt/test2/mkfs-test/4tfile-ext4 > 4294967296 67592304 4012626628 2% /mnt/test2/mkfs-test/4t-ext4 > > I'd say this appears to be a slight inaccuracy in ext4_statfs, coupled with > the strangeness of the "bsd df" reporting. It is apparently miscalculating > the filesystem metadata "overhead." > >> I performed the same on XFS and the result was: >> 1TB: 32928 >> 4TB: 32928 >> 7TB: 33024 > > XFS is straightforward; blocks used for metadata count as "used." > Every other block is free and available. > No fiddling around, just like with the minixdf mount option for extN. > > -Eric > >> EXT4 result shows with increasing filesystem size, the number of used >> blocks decreased. I dont have idea about low level implementation but >> I am curious why it is so? >> >> Thanks. >> >> Regards, >> Adil >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
