On Oct 16, 2014, at 10:25 AM, Bodo Thiesen <bothie@xxxxxx> wrote: > * Andreas Dilger <adilger@xxxxxxxxx> hat geschrieben: > >> You can see in the ext4 superblock the amount of data that has been >> written to a filesystem over its lifetime: >> >> Note that this number isn't wholly accurate, but rather a guideline. > > Is is more like a completely bogus value at best: > > # LANG=C df -h / | grep root > /dev/root 3.7T 3.6T 73G 99% / > # grep [0-9] /proc/partitions > 8 0 3907018584 sda > # tune2fs -l /dev/sda | grep Lifetime > Lifetime writes: 2503 GB > > 3.7 TB Disk/Partition, 3.6 TB space in use but only 2.4 TB writes. > > No, there are no 1.2 TB + x allocated but never written to clusters on > that file system. > > And if /sys/fs/ext4/*/*_write_kbytes are as correct as the "Lifetime > writes" value, than the correct answer to Jelle's question is: "There is > no way currently to figure out the actual number of writes to a device". The "lifetime writes" value has not been around forever, so if the filesystem was originally created and populated on an older kernel (e.g. using ext3) it would not contain a record of those writes. There is also some potential loss if the filesystem isn't unmounted cleanly. It definitely _can_ be used to monitor the writes to a particular filesystem over the past 24h, which is what the original poster was asking about. Cheers, Andreas
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