From 53cbac409bd5077aae26c22f51d2af3fb0f87ff8 Mon Sep 17 00:00:00 2001 From: Nick Chevsky Date: Wed, 14 Nov 2018 12:16:03 -0500 Subject: [PATCH] Remove SCSI exclusivity from "Discard" drive option This documents the recent move [1] to make the formerly SCSI-exclusive "Discard" option also available to IDE and SATA drives, and explains its dependency on either VirtIO SCSI or SSD emulation [2]. [1] https://git.proxmox.com/?p=pve-manager.git;a=commit;h=ee4b837692bf3d0f50b6cb8f29a5272e9a632430 [2] https://git.proxmox.com/?p=pve-docs.git;a=commit;h=25203dc111c1af5a1e100246954d1467535676c7 Signed-off-by: Nick Chevsky --- qm.adoc | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/qm.adoc b/qm.adoc index 0d453c8..a15e0fe 100644 --- a/qm.adoc +++ b/qm.adoc @@ -193,16 +193,21 @@ As of {pve} 5.0, replication requires the disk images to be on a storage of type configured requires to skip replication for this disk image. If your storage supports _thin provisioning_ (see the storage chapter in the -{pve} guide), and your VM has a *SCSI* controller you can activate the *Discard* -option on the hard disks connected to that controller. With *Discard* enabled, -when the filesystem of a VM marks blocks as unused after removing files, the -emulated SCSI controller will relay this information to the storage, which will -then shrink the disk image accordingly. +{pve} guide), you can activate the *Discard* option on a drive. With *Discard* +set and a _TRIM_-enabled guest OS footnote:[TRIM, UNMAP, and discard +https://en.wikipedia.org/wiki/Trim_%28computing%29], when the VM's filesystem +marks blocks as unused after deleting files, the controller will relay this +information to the storage, which will then shrink the disk image accordingly. +For the guest to be able to issue _TRIM_ commands, you must either use a +*VirtIO SCSI* (or *VirtIO SCSI Single*) controller or set the *SSD emulation* +option on the drive. Note that *Discard* is not supported on *VirtIO Block* +drives. If you would like a drive to be presented to the guest as a solid-state drive rather than a rotational hard disk, you can set the *SSD emulation* option on that drive. There is no requirement that the underlying storage actually be backed by SSDs; this feature can be used with physical media of any type. +Note that *SSD emulation* is not supported on *VirtIO Block* drives. .IO Thread The option *IO Thread* can only be used when using a disk with the -- 2.39.2