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Bug 1498955

Summary:	RFE: option to mark virtual block device as rotational/non-rotational
Product:	Red Hat Enterprise Linux Advanced Virtualization	Reporter:	Daniel Berrangé <berrange>
Component:	libvirt	Assignee:	Daniel Berrangé <berrange>
Status:	CLOSED ERRATA	QA Contact:	Han Han <hhan>
Severity:	high	Docs Contact:
Priority:	high
Version:	8.0	CC:	berrange, coli, dyuan, eblake, jdenemar, jsuchane, kchamart, knoel, mailinglists35, markmc, qinwang, rbalakri, rkant, thomas, virt-bugs, virt-maint, xuzhang
Target Milestone:	rc	Keywords:	FutureFeature, Reopened, Triaged
Target Release:	8.0	Flags:	areis: mirror+
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	libvirt-7.3.0-1.el8	Doc Type:	Enhancement
Doc Text:		Story Points:	---
Clone Of:	1498042	Environment:
Last Closed:	2021-11-16 07:49:54 UTC	Type:	Feature Request
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:	7.3.0
Embargoed:
Bug Depends On:	1498042, 1664302
Bug Blocks:

Description Daniel Berrangé 2017-10-05 15:47:01 UTC

Cloning QEMU bug to libvirt to track exposing this in <disk> XML.

+++ This bug was initially created as a clone of Bug #1498042 +++

Description of problem:
In absence of information to the contrary, Linux guests assume that all block devices are backed by rotational storage. The guest OS admin can override this by setting the 'rotational' flag in sysfs.

It would be desirable to be able to inform the guest OS the correct rotational/non-rotational setting based on what is used as the backing for the virtual block device.

In Linux, if a disk is marked non-rotational disk, it is also removed as a source of random entropy, so if a virtual disk is backed by SSD it is desirable that the guest know this so that it doesn't consider it an entropy source.

Both ATA and SCSI protocols have a way to report this feature.

For SCSI the Block Device Characteristics VPD, page 0xb1 provides a flag that Linux checks:

        if (!buffer ||
            /* Block Device Characteristics VPD */
            scsi_get_vpd_page(sdkp->device, 0xb1, buffer, vpd_len))
                goto out;

        rot = get_unaligned_be16(&buffer[4]);

        if (rot == 1) {
                queue_flag_set_unlocked(QUEUE_FLAG_NONROT, q);
                queue_flag_clear_unlocked(QUEUE_FLAG_ADD_RANDOM, q);
        }


For ATA there is an ID flag with the info that Linux checks

        ATA_ID_ROT_SPEED        = 217,

static inline bool ata_id_is_ssd(const u16 *id)
{
        return id[ATA_ID_ROT_SPEED] == 0x01;
}



virtio-blk has no mechanism for this. One could be added, or just rely on a recommendation use of virtio-scsi instead.

So QEMU would need to have a 'rotational' boolean flag added for its SCSI & ATA disk device backends. Libvirt would in turn expose this setting to mgmt apps, which would set it based on their knowledge of the storage in use.

--- Additional comment from Eric Blake on 2017-10-03 13:02:37 BST ---

NBD also supports the advertisement of rotational or not

--- Additional comment from Daniel Berrange on 2017-10-03 13:05:49 BST ---

(In reply to Eric Blake from comment #3)
> NBD also supports the advertisement of rotational or not

Interestingly/strangely the Linux NBD kernel client ignores this feature, and unconditionally sets the block dev as non-rotational.

--- Additional comment from Daniel Berrange on 2017-10-04 12:52:54 BST ---

Posted some possible patches for IDE/SCSI https://lists.gnu.org/archive/html/qemu-devel/2017-10/msg00698.html

Comment 3 Erik Skultety 2019-01-07 12:49:12 UTC

In order to implement this properly, libvirt needs to be able to QAPI introspect device options. Once we can query for the rotation_rate property, it's fairly simple to expose it as an attribute within the XML.

Comment 4 Erik Skultety 2020-10-05 10:21:08 UTC

*** Bug 1595931 has been marked as a duplicate of this bug. ***

Comment 7 RHEL Program Management 2021-01-15 07:43:14 UTC

After evaluating this issue, there are no plans to address it further or fix it in an upcoming release.  Therefore, it is being closed.  If plans change such that this issue will be fixed in an upcoming release, then the bug can be reopened.

Comment 12 Daniel Berrangé 2021-03-31 09:52:04 UTC

Support for setting rotation rate is proposed here https://listman.redhat.com/archives/libvir-list/2021-March/msg01438.html

Comment 13 Daniel Berrangé 2021-04-01 14:40:35 UTC

This is now merged upstream

commit 8dac0ca1b259c53d09983fe09f935baa18eb416c
Author: Daniel P. Berrangé <berrange>
Date:   Wed Mar 31 10:17:07 2021 +0100

    qemu: implement setting of rotation rate for SCSI/IDE disks
    
    This is available in QEMU with "ide-hd" and "scsi-hd" device
    types. It was originally mistakenly added to the "scsi-block"
    device type too, but later removed. This doesn't affect libvirt
    since we restrict usage to device=disk.
    
    When this property is not set then QEMU's default behaviour
    is to not report any rotation rate information, which
    causes most guest OS to assume rotational storage.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1498955
    
    Reviewed-by: Ján Tomko <jtomko>
    Signed-off-by: Daniel P. Berrangé <berrange>

commit feac14fa2e7cc737a0f5920fab531602703d2a13
Author: Daniel P. Berrangé <berrange>
Date:   Wed Mar 31 10:14:12 2021 +0100

    conf: add support for disk "rotation_rate" property
    
    This lets the app expose the virtual SCSI or IDE disks as solid state
    devices by setting a rate of '1', or rotational media by setting a
    rate between 1025 and 65534.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1498955
    
    Reviewed-by: Ján Tomko <jtomko>
    Signed-off-by: Daniel P. Berrangé <berrange>


This will become part of a future 7.3.0 libvirt release, so will get it automatically upon a rebase.

Comment 14 Han Han 2021-04-27 09:34:43 UTC

Tested https://listman.redhat.com/archives/libvir-list/2021-April/msg00000.html

Comment 18 Han Han 2021-05-18 09:52:08 UTC

Test on libvirt-7.3.0-1.module+el8.5.0+11004+f4810536.x86_64 qemu-kvm-6.0.0-16.module+el8.5.0+10848+2dccc46d.x86_64 

Steps
1. Start VM with ide/sata disk and set the rotation_rate
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/var/lib/libvirt/images/hda' index='2'/>
      <backingStore/>
      <target dev='hda' bus='ide' rotation_rate='5400'/>
      <alias name='ide0-0-0'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/var/lib/libvirt/images/sdb' index='1'/>
      <backingStore/>
      <target dev='sdb' bus='sata' rotation_rate='5500'/>
      <alias name='sata0-0-1'/>
      <address type='drive' controller='0' bus='0' target='0' unit='1'/>
    </disk>

2. Hot-plug scsi disk with rotation_rate

3. Check the rotation_rate inside the VM by `smartctl -i /dev/sdX`

All pass

Comment 20 errata-xmlrpc 2021-11-16 07:49:54 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (virt:av bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2021:4684