Hi, > My only point is, default ext4 statfs behavior is quite complicated, and it > looks like you have found a bug related to the calculation of metadata overhead. I see. Where should I report this issue to get it confirm by developers? > It should only be a reporting issue, and should not cause any runtime issues. OK, I understand. Thanks, Adil On Mon, Feb 11, 2013 at 11:02 PM, Eric Sandeen <sandeen@xxxxxxxxxx> wrote: > On 2/11/13 12:36 AM, Adil Mujeeb wrote: >> 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 :( > > My only point is, default ext4 statfs behavior is quite complicated, and it > looks like you have found a bug related to the calculation of metadata overhead. > > It should only be a reporting issue, and should not cause any runtime issues. > > Thanks, > -Eric > >> 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
