transform virtio-blk to scsi-virtio

[Afox]

Hello,
I just realized I can´t use the discard option with my virtio block device and want to "transform" the storage to a SCSI-virtio device.

Is there a painless and save way to do this?

Thanks in advance,

Afox

 

[dietmar]

Simply remove the drives, then re-add the volumes using the correct driver.

 

[Afox]

thank you so much

 

[Afox]

on Windows it gives me bluescreen(s). Is there a special way I need to do it there?

Edit:
I made it work as follows:

1. shutdown the VM and add an extra SCSI-virtio drive
2. boot the VM and install the driver (device manager)
3. shutdown the VM and remove the extra drive
4. change the desired drive to SCSI-virtio and start again

 

[Klaus Steinberger]

yes, the extra dummy drive is the way to have it work in windows.

 

[Afox]

I have another phenomenon that exist with a newly created VM.
On install it recognized the "old" virtio drive as /dev/vdX. Now, when I change to SCSI-virtio, it gets somehow changed to /dev/sdX and does not boot anymore because it can´t find the /dev/vdX device.

 

[Klaus Steinberger]

a Linux VM? hard coded /dev/vdX in the fstabs?

Try changing mounts to uuid style and the recreate the initramfs

 

[Afox]

somehow it is hardcoded in the grub bootloader. I am not quite sure how to fix this.

Edit: It turns out running

update-grub

did the trick before changing the device. Then the hardcoded device became an UUID.

If it is too late to do this, reboot the VM and press "E" to edit the grub options manually. Change the device name (e.g. /dev/vdX to /dev/sdX) manually and then log in and run the command above.

if you don´t know how the device got renamed, use the initramfs-shell you got stuck in and run

blkid

to find out the new name.

 

[Klaus Steinberger]

which distribution is it?

depending on the distribution you can change it in /boot/grub/grub.conf (oldish grub1) or with ubuntu "update-grub" will fix it

 

[Afox]

it is Debian 9 and what I read it is not recommended to edit the grub.cfg file manually. update-grub did the trick so far

 

[Klaus Steinberger]

yep, that's same as in ubuntu

 

[Afox]

ok, thank you
meanwhile I also changed a Windows 7 guest, enabled the discard option, got a "0" when running

fsutil behavior query DisableDeleteNotify

but still am not sure if it is working and how to run it (TRIM) once manually.

I found a command for PowerShell but it does not seem to be working for Windows 7:

Optimize-Volume -DriveLetter C -ReTrim -Verbose

It gives me a CommandNotFoundException.

 

[aderumier]

ok, thank you
meanwhile I also changed a Windows 7 guest, enabled the discard option, got a "0" when running

but still am not sure if it is working and how to run it (TRIM) once manually.

I found a command for PowerShell but it does not seem to be working for Windows 7:

Optimize-Volume -DriveLetter C -ReTrim -Verbose

It gives me a CommandNotFoundException.

it's only supported since win8/2012. (maybe 8.1,2012r2)

(you also have a gui, "optimize disk")

 

[Afox]

is there nevertheless any way to make trim work on Windows 7? Because on my Guest it doesn´t look like the drive is even recognized as SSD which in consequence does not enable TRIM.
I tested with this tool: https://github.com/CyberShadow/trimcheck

 

[Klaus Steinberger]

Too bad, no. Windows 7 supports discard only with s-ata trim Command, which is not supported in qemu sata.

The SCSI unmap Command is only supported with Windows 8 and newer versions.

I searched for Utilities, but with no success. There is One from VMware, but it had no Effect with virtio-scsi. It probably needs some special features from VMware. There was one from EMC but development has ceased 2013 and is not anymore available even with an EMC contract.

If somebody knows an working Utility, i would be glad, as I have some win7 as well as some win 2008r2 vm's.

 

[Afox]

maybe there is an alternative way to do this occasionally?
Maybe to run SDelete like mentioned here: https://pve.proxmox.com/wiki/Shrink_Qcow2_Disk_Files#Zero_Using_SDelete

 

[Klaus Steinberger]

At least with CEPH in the background it will not help (just tested it).

 

[Afox]

did you make a backup before and after? for me it noticably reduced the backup size.

 

[Klaus Steinberger]

I looked into the "rbd du" command, no change here.
As sdelete zeroes blocks, this could of course help with backups and qcow

 

[Progratron]

The method still works Remember to change the Boot device in the options though: