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Remove SCSI exclusivity from "Discard" drive option

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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 <nchevsky@gmail.com>
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Nick Chevsky 2018-11-14 12:16:03 -05:00 committed by Thomas Lamprecht
parent 1121e9ca86
commit 53cbac409b
1 changed files with 10 additions and 5 deletions
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@ -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