Revision as of 14:14, 29 January 2013

Block Device Configuration

Controls for block device configuration

There are a variety of independent attributes that it is desirable to control when configuring block devices for a virtual machine in OpenStack

Source type

• Glance image
• Cinder volume
• Ephemeral file

Guest format

• ext4 (or other FS formats)
• ISO
• Swap (different format per guest OS)
• None

Device type

• Disk
• CDROM
• Floppy
• Flash (MMC)

Disk bus

• USB
• IDE
• VirtIO
• SCSI

Shutdown action

• Delete
• Preserve

Boot order

• Index

In addition to the above parameters, it is neccesary to support a "disk path" parameter, to allow the user to request a specific block device path in the guest eg /dev/sda. In general this cannot be supported by all hypervisors and thus its usage should be discouraged in favour of allowing the guest OS / hypervisor to choose paths. For the sake of compatibility with existing tools / APIs though, it must be supported

Command line syntax for block config

The 'nova boot' command currently uses a combination of the '-image' and '-block-device-mapping' command line args to configure storage. The latter is mostly a clone of the same named arg from the EC2 commands, and is not a very well designed syntax from the POV of extensibility.

Given the extra features to be supported, it is desirable to introduce a new syntax for 'nova boot' and friends which is more expressive

• -block type=glance,id=XXXXXXX,bus=ide,bootindex=2
• -block type=cinder,id=XXXXXXX,bus=ide,device=cdrom,bootdex=1
• -block type=ephemeral,format=swap,size=50,bus=ide,device=floppy

The only compulsory argument ought to be the type + id, eg the glance or cinder ID. Everything else should have sane defaults filled in by the hypervisor driver in Nova.

Possible parameters would be

• type=glance|cinder|ephemeral
• id=XXXXXX (a volume/image UUID if using type=glance or type=cinder)
• format=swap|ext4|...|none (to format the image/volume/ephemeral file; defaults to 'none' if omitted)
• bus=ide|usb|virtio|scsi (hypervisor driver chooses a suitable default if omitted)
• device=disk|cdrom|floppy|mmc (defaults to 'disk' if omitted)
• bootindex=N (where N is any number >= 0, controls the order in which disks are looked at for booting)
• size=NN (where NN is number of GB to create type=emphemeral image, or the size to re-size to for type=glance|cinder)
• shutdown=preserve|remove (where the default is remove for type=glance|ephemeral or preserve for type=cinder)

Data Format for Nova Compute APIs

TBD