I'm trying to display I/O data from /proc/diskstats for regular, non-thin partitions, by lv_name. "-cow" and "-real" bit confusing. When I look at the output of "dmsetup ls" different minor devs for: name minor Home-real 2 Home 3 Home-snapshot 5 Home-snapshot-cow 26 (snapshot=date+time snapshot was started) I regularly see I/O on 'Home' & 'Home-real'. write = "dd if=/dev/zero of=1G bs=1G count=1 oflag=direct" A 1G write to Home shows 2GB I/O on 2 partitions: Home: 1G read Home-real: 1G read Is this being double reported? (i.e. I should ignore one?) Confusing is that they don't always show the same amount of I/O. A write to the same filename again showed 4GB I/O on 3 partitions: Home: 1G read + 1G write Home-real: 1G write Home-snap-cow: 1G write Is there some read is copying off the first copy to the "cow" partition? (with a 1G duplication somewhere?). If I "overwrite" (dd if=/dev/zero of=1G bs=1G count=1 oflag=direct conv=nocreat) I see the same numbers as on the initial file creation (to both base and the "-real" partitions). Could anyone clarify what's going on in the above scenarios? (i.e. I would find each write being multiplied by 2 a bit far fetched in terms of disk-BW; Multiplied by 4... even less likely I'd think...? Thanks for any light-shed...;-) _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
