add paragraph for IO Thread option

[pve-docs.git] / qm.adoc

diff --git a/qm.adoc b/qm.adoc
index ab6d5bd53edf69c7cd10f792003e9f675b2c2e42..f6c968adc7931ef1dabbd4b7f4a398bbdcfb7b3a 100644 (file)
--- a/qm.adoc
+++ b/qm.adoc
@@ -162,6 +162,12 @@ 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.
 
+The option *IO Thread* can only be enabled when using a disk with the *Virtio* controller,
+or with the *SCSI* controller, when the emulated controller type is *VIRTIO*.
+With this enabled, Qemu uses one thread per disk, instead of one thread for all,
+so it should increase performance when using multiple disks.
+Note that backups do not currently work with *IO Thread* enabled.
+
 Managing Virtual Machines with 'qm'
 ------------------------------------