Bug#717313: lvm2: Enable issue_discards = 1 automatically on non-rotational (SSD) disks?

[Laurent Bigonville]

Le 06/08/17 à 12:55, Petter Reinholdtsen a écrit :
> [Laurent Bigonville]
>> The discards commands will also be issued when shrinking or moving a LV
>> to an other PV, if something is going wrong during these operations, the
>> data will be lost.
>>
>> So it's not only when explicitly removing an LV.
> Aha.  I did not have the imagination required to consider that such
> commands would be issued before the operation was sccessfully completed.
> It seemed to me quite obvious that the space would be released only
> after the shrink or move was complete, but if that is not the case, it
> seem quite unsafe to trust LVM to handle discard commands.
>
I got hit with a bug while migrating my data from my old non-ssd to ssd 
drive. In the end I had no data on the SSD (apparently LVM was issuing 
discards on the destination disk...) and the LV was deleted from the 
non-ssd one. Hopefully the data were still on the old disk (as it was 
not supporting DISCARD) so I was able to recover the LV.

While this bug is fixed now, with that kind of experience I can 
understand why upstream wants to be on the safe side here.