i'm sorry to bother you again with my ignorance of the DISCARD feature
for block devices in general.
after finding several ways to enable "discard=unmap" for oVirt disks
(via standard GUI option for iSCSI disks or via "diskunmap" custom
property for Cinder disks) i wanted to check in the guest for the
effectiveness of this feature. to my surprise i couldn't find a
difference between Linux guests with and without "discard=unmap" enabled
in the VM. "lsblk -D" reports the same in both cases and also
fstrim/blkdiscard commands appear to work with no difference. Why is
this? Do i have to look at the underlying storage to find out what
really happens? Shouldn't this be visible in the guest OS?
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