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Attaching volumes

Capstan supports attaching any number of pre-prepared volumes to the instance. Currenly, you need to prepare a volume manually i.e. with external tools, and then export it into a file on your host. During the capstan run you then provide path to this file together with some metadata.

NOTE: volumes are only supported for QEMU hipervisor at the moment.

Creating a new volume

You can create a new volume with Capstan:

$ capstan volume create volume1

The command above will create a volume of size 1GB in RAW format by default. Consult capstan volume create --help to learn how other size or other formats can be used. The volume will be created as ./volumes/volume1.

Attaching volumes

Tell Capstan where your volume is and it will attach it to the instance on run:

$ capstan run demo --volume ./volumes/volume1

The volume will get attached as /dev/vblk1 into the unikernel. The --volume argument can be repeated to attach multiple volumes:

$ capstan run demo --volume ./volume1 --volume ./volume2 --volume ./volume3

Volumes will get attached as /dev/vblk1, /dev/vblk2, /dev/vblk3 in the same order as provided (left-to-right).

Volume metadata

You can provide volume metadata for Capstan to be able to attach it as desired:

$ capstan run demo --volume ./volume1:format=qcow2:aio=threads

KEY	DEFAULT VALUE	VALUES
format	raw	raw,qcow2,vdi,vmdk
aio	native	native/threads
cache	none	none/writeback/writethrough/directsync/unsafe

Consult QEMU documentation for more details.