Fix #2459: qm: Make info about core limit clear

[pve-docs.git] / qm.adoc

diff --git a/qm.adoc b/qm.adoc
index 429cff614ad5fd64f614bdd72e72c9eed8e9bd44..b13f0f4ccb419222bb8dd3729e77801eb515a5a0 100644 (file)
--- a/qm.adoc
+++ b/qm.adoc
@@ -150,6 +150,9 @@ one want's to pass through PCIe hardware.
 Hard Disk
 ~~~~~~~~~
 
+[[qm_hard_disk_bus]]
+Bus/Controller
+^^^^^^^^^^^^^^
 Qemu can emulate a number of storage controllers:
 
 * the *IDE* controller, has a design which goes back to the 1984 PC/AT disk
@@ -182,6 +185,10 @@ is an older type of paravirtualized controller. It has been superseded by the
 VirtIO SCSI Controller, in terms of features.
 
 [thumbnail="screenshot/gui-create-vm-hard-disk.png"]
+
+[[qm_hard_disk_formats]]
+Image Format
+^^^^^^^^^^^^
 On each controller you attach a number of emulated hard disks, which are backed
 by a file or a block device residing in the configured storage. The choice of
 a storage type will determine the format of the hard disk image. Storages which
@@ -200,6 +207,9 @@ either the *raw disk image format* or the *QEMU image format*.
  * the *VMware image format* only makes sense if you intend to import/export the
  disk image to other hypervisors.
 
+[[qm_hard_disk_cache]]
+Cache Mode
+^^^^^^^^^^
 Setting the *Cache* mode of the hard drive will impact how the host system will
 notify the guest systems of block write completions. The *No cache* default
 means that the guest system will be notified that a write is complete when each
@@ -215,6 +225,9 @@ As of {pve} 5.0, replication requires the disk images to be on a storage of type
 `zfspool`, so adding a disk image to other storages when the VM has replication
 configured requires to skip replication for this disk image.
 
+[[qm_hard_disk_discard]]
+Trim/Discard
+^^^^^^^^^^^^
 If your storage supports _thin provisioning_ (see the storage chapter in the
 {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
@@ -232,14 +245,16 @@ 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
+
+[[qm_hard_disk_iothread]]
+IO Thread
+^^^^^^^^^
 The option *IO Thread* can only be used when using a disk with the
 *VirtIO* controller, or with the *SCSI* controller, when the emulated controller
  type is  *VirtIO SCSI single*.
 With this enabled, Qemu creates one I/O thread per storage controller,
-instead of a single thread for all I/O, so it increases performance when
-multiple disks are used and each disk has its own storage controller.
-Note that backups do not currently work with *IO Thread* enabled.
+instead of a single thread for all I/O, so it can increase performance when
+multiple isks are used and each disk has its own storage controller.
 
 
 [[qm_cpu]]
@@ -268,8 +283,8 @@ is greater than the number of cores on the server (e.g., 4 VMs with each 4
 cores on a machine with only 8 cores). In that case the host system will
 balance the Qemu execution threads between your server cores, just like if you
 were running a standard multithreaded application. However, {pve} will prevent
-you from assigning more virtual CPU cores than physically available, as this will
-only bring the performance down due to the cost of context switches.
+you from starting VMs with more virtual CPU cores than physically available, as
+this will only bring the performance down due to the cost of context switches.
 
 [[qm_cpu_resource_limits]]
 Resource Limits
@@ -856,6 +871,8 @@ Select the folder to share and then enable the checkbox.
 
 NOTE: Folder sharing currently only works in the Linux version of Virt-Viewer.
 
+CAUTION: Experimental! Currently this feature does not work reliably.
+
 Video Streaming
 ^^^^^^^^^^^^^^^