Create VM Hard Disk Option

[JasonC]

I'm looking for some clarification on a few of the Hard Disk settings when configuring a Hard Disk for a VM using Proxmox 4.0-50.

Bus/Device? IDE / SATA / VIRTIO / SCSI

I've read in a few places that everyone believes that VirtIO for linux instances are the way to go? Any comments on the others in comparison? If someone has a document on the advantages / disadvantages to them, i'd love to read it.

No backup?

Discard? Is this about hole punching a using trim to keep the file on the host smaller?

Iothread?

I believe I have figured out what Iothread is for after reading a few sites on the net, but what about the other two? I'd love to understand more what those options actually mean...

Thanks in advance, and my apologies if this is posted some where else, i have searched the forums here and have not found anything directly related to the no backup, discard, and iothread options specifically..

 

[manu]

Hi Jason
Bus/Device? IDE / SATA / VIRTIO / SCSI

Yes virtio is the way to go. See http://events.linuxfoundation.org/sites/events/files/slides/CloudOpen2013_Khoa_Huynh_v3.pdf
Page 9.

Discard: makes only sense if you have SSDs.

No backup: the hard drive will not be included in backups.

Iothreads should speed up your IO, but currently it prevents disk from being backed up.

 

[mir]

Discard: makes only sense if you have SSDs.

This is not the complete story. Discard is relevant for all storage backends which supports SATA trim or SCSI unmap but for performance and longevity it is more wisely to disable automatic trim/unmap from every delete operation and do this in a cronjob instead. Trim/unmap is a fundamental requirement for thin provisioning since otherwise storage requirements will rise astronomically - release of sectors by the file system will never reach the underlying storage.

 

[Mitya]

Actually, Discard actually frees space in many thin-provisioned storages, like qcow2 files and ceph rbd.