Re: Should issue_discards be enabled when e2scrub is used on an SSD?

[Zdenek Kabelac <zdenek.kabelac@gmail.com>]

Dne 29. 12. 23 v 1:48 Mikhail Morfikov napsal(a):
> I've got the following setup: LUKSv2+LVM on an SSD drive, and I have 
> trim/discad enabled
> for encrypted container. I also use e2scrub for Online ext4 Metadata Check 
> which uses a 4
> GiB LVM snapshot. I currently have 10 logical volumes, which are periodically 
> (once a week)
> scanned for errors. I've got a question concerning the *issue_discards* option 
> that can be
> specified in the /etc/lvm/lvm.conf file. What actually happens when this 
> option is enabled
> and the LVM snapshot is removed after fsck finishes its job? Will the whole 4 
> GiB be erased
> on the flash? Is it safe to enable this option in such case, or is it better 
> to leave it
> disabled?

Hello

issue_discards  is relevant only when you *REMOVE* LVs  - the free space in VG 
  is after such removal 'discarded' - which is only useful in case you i.e. 
pay for 'provisioned' space for your VG (or you have some very very very old 
ssd) - so this will make you VG space consumption smaller - but it will also 
make restoring of accidentally removed LVs impossible as the recovered LV will 
be simply just an empty disk space.

So for 100% you don't need to enabled it for e2scrub as discards are normally 
passed through to your LV device as you may easily check in your sysfs dir:

/sys/block/XXXX/queue/discard_max_bytes

Regards

Zdenek