Discussion:
[pve-devel] integration of scsi-hd, scsi-block, scsi-generic
Stefan Priebe
2012-08-11 21:03:35 UTC
Permalink
Hello list,

right now when you select SCSI proxmox always use scsi-hd for device.
With virtio-scsi-pci as scsihw we can also select scsi-block or
scsi-generic.

With scsi-block and scsi-generic you can bypass qemu scsi emulation and
use trim / discard support as the guest can talk directly to the
underlying storage.

Also scsi-generic (needs guest kernel 3.4) is a lot faster then scsi-hd
or scsi-block.

What would be the expected way to integrate a selection between them in
proxmox?

Greets,
Stefan
Alexandre DERUMIER
2012-08-11 23:27:18 UTC
Permalink
Post by Stefan Priebe
right now when you select SCSI proxmox always use scsi-hd for device.
not totally true, we use scsi-block if device is an scsi device on host.
(but indeed with libiscsi it's always scsi-hd)
Post by Stefan Priebe
Also scsi-generic (needs guest kernel 3.4) is a lot faster then scsi-hd
or scsi-block.
does scsi-block works with libiscsi with kvm 1.1 ? (so we can select it by default is we use libiscsi)


about scsi-generic, what happen is the guest has a kernel < 3.4 ?


----- Mail original -----

De: "Stefan Priebe" <***@profihost.ag>
À: pve-***@pve.proxmox.com
Envoyé: Samedi 11 Août 2012 23:03:35
Objet: [pve-devel] integration of scsi-hd, scsi-block, scsi-generic

Hello list,

right now when you select SCSI proxmox always use scsi-hd for device.
With virtio-scsi-pci as scsihw we can also select scsi-block or
scsi-generic.

With scsi-block and scsi-generic you can bypass qemu scsi emulation and
use trim / discard support as the guest can talk directly to the
underlying storage.

Also scsi-generic (needs guest kernel 3.4) is a lot faster then scsi-hd
or scsi-block.

What would be the expected way to integrate a selection between them in
proxmox?

Greets,
Stefan
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--
Alexandre D e rumier

Ingénieur Systèmes et Réseaux


Fixe : 03 20 68 88 85

Fax : 03 20 68 90 88


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12 rue Marivaux 75002 Paris
Stefan Priebe
2012-08-12 08:14:17 UTC
Permalink
Post by Alexandre DERUMIER
Post by Stefan Priebe
Also scsi-generic (needs guest kernel 3.4) is a lot faster then scsi-hd
or scsi-block.
does scsi-block works with libiscsi with kvm 1.1 ? (so we can select it by default is we use libiscsi)
scsi-block does not even work with current ;-) qemu.git as there is a
bug. But it will be fixed for qemu 1.2. But anyway scsi-generic is much
more interesting. It's a lot faster.
Post by Alexandre DERUMIER
about scsi-generic, what happen is the guest has a kernel < 3.4 ?
Haven't tested but as virtio-scsi-pci was introduced in 3.2 anyway i
won't care much about older kernels. What do you thik? (i mean 3.4 is
not far away from 3.2)

Greets,
Stefan
Alexandre DERUMIER
2012-08-12 09:05:31 UTC
Permalink
I have tested both, thet don't works with kvm 1.1

scsi-block


kvm: -device scsi-block,bus=scsihw0.0,scsi-id=0,drive=drive-scsi0,id=scsi0: scsi-block: scsi generic interface too old
kvm: -device scsi-block,bus=scsihw0.0,scsi-id=0,drive=drive-scsi0,id=scsi0: Device 'scsi-block' could not be initialized


scsi-generic

kvm: -device scsi-generic,bus=scsihw0.0,scsi-id=0,drive=drive-scsi0,id=scsi0: not /dev/sg*
kvm: -device scsi-generic,bus=scsihw0.0,scsi-id=0,drive=drive-scsi0,id=scsi0: Device 'scsi-generic' could not be initialized
Post by Alexandre DERUMIER
about scsi-generic, what happen is the guest has a kernel < 3.4 ?
Haven't tested but as virtio-scsi-pci was introduced in 3.2 anyway i
won't care much about older kernels. What do you thik? (i mean 3.4 is
not far away from 3.2)

Yes I think we can put scsi-generic as default when using libiscsi, but we need to wait for kvm 1.2 (should come in 1 or 2 month)

If you really need it , you can hack /usr/share/perl5/PVE/QemuServer.pm, sub print_drivedevice_full , my $devicetype = 'hd' -> generic.



----- Mail original -----

De: "Stefan Priebe" <***@profihost.ag>
À: "Alexandre DERUMIER" <***@odiso.com>
Cc: pve-***@pve.proxmox.com
Envoyé: Dimanche 12 Août 2012 10:14:17
Objet: Re: [pve-devel] integration of scsi-hd, scsi-block, scsi-generic
Post by Alexandre DERUMIER
Post by Stefan Priebe
Also scsi-generic (needs guest kernel 3.4) is a lot faster then scsi-hd
or scsi-block.
does scsi-block works with libiscsi with kvm 1.1 ? (so we can select it by default is we use libiscsi)
scsi-block does not even work with current ;-) qemu.git as there is a
bug. But it will be fixed for qemu 1.2. But anyway scsi-generic is much
more interesting. It's a lot faster.
Post by Alexandre DERUMIER
about scsi-generic, what happen is the guest has a kernel < 3.4 ?
Haven't tested but as virtio-scsi-pci was introduced in 3.2 anyway i
won't care much about older kernels. What do you thik? (i mean 3.4 is
not far away from 3.2)

Greets,
Stefan
--
--
Alexandre D e rumier

Ingénieur Systèmes et Réseaux


Fixe : 03 20 68 88 85

Fax : 03 20 68 90 88


45 Bvd du Général Leclerc 59100 Roubaix
12 rue Marivaux 75002 Paris
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