[PVE-User] Discard transmission between VM / LVM / mdadm layers ?

Michael Rasmussen mir at miras.org
Sun Dec 15 13:13:21 CET 2019

On Sun, 15 Dec 2019 12:51:01 +0100
Frédéric MASSOT <frederic at juliana-multimedia.com> wrote:

> Le 13/12/2019 à 13:15, Alexandre DERUMIER a écrit :
> > When a VM sends a discard/trim command, is it sent to the SSD, LVM
> > does not block the command?
> > 
> > Hi, yes it's working with lvm (lvm thin only)  
> Hi,
> I opened a bug report to the debian-installer package to see if it
> could add lvm-thin support.
LVM supports discard so there is no need to change to lvm-thin for that

From lvm.conf:
"        # Configuration option devices/issue_discards.
        # Issue discards to PVs that are no longer used by an LV.
        # Discards are sent to an LV's underlying physical volumes when
the LV # is no longer using the physical volumes' space, e.g. lvremove,
        # lvreduce. Discards inform the storage that a region is no
longer # used. Storage that supports discards advertise the
protocol-specific # way discards should be issued by the kernel (TRIM,
UNMAP, or # WRITE SAME with UNMAP bit set). Not all storage will
support or # benefit from discards, but SSDs and thinly provisioned LUNs
        # generally do. If enabled, discards will only be issued if
both the # storage and kernel provide support.
        issue_discards = 0

Michael Rasmussen

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