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From Rafael Weingärtner <>
Subject Re: Attaching more than 14 data volumes to an instance
Date Wed, 15 Feb 2017 16:27:27 GMT
I hate to say this, but probably no one knows why.
I looked at the history and this method has always being like this.

The device ID 3 seems to be something reserved, probably for Xen tools (big
guess here)?

Also, regarding the limit; I could speculate two explanations for the
limit. A developer did not get the full specs and decided to do whatever
he/she wanted. Or, maybe, at the time of coding (long, long time ago) there
was a hypervisor that limited (maybe still limits) the number of devices
that could be plugged to a VM and the first developers decided to level
everything by that spec.

It may be worth checking with KVM, XenServer, Hyper-V, and VMware if they
have such limitation on disks that can be attached to a VM. If they do not
have, we could remove that, or at least externalize the limit in a

On Wed, Feb 15, 2017 at 5:54 AM, Friðvin Logi Oddbjörnsson <> wrote:

> CloudStack is currently limiting the number of data volumes, that can be
> attached to an instance, to 14.
> More specifically, this limitation relates to the device ids that
> CloudStack considers valid for data volumes.
> In method VolumeApiServiceImpl.getDeviceId(long, Long), only device ids 1,
> 2, and 4-15 are considered valid.
> What I would like to know is: is there a reason for this limitation? (of
> not going higher than device id 15)
> Note that the current number of attached data volumes is already being
> checked against the maximum number of data volumes per instance, as
> specified by the relevant hypervisor’s capabilities.
> E.g. if the relevant hypervisor’s capabilities specify that it only
> supports 6 data volumes per instance, CloudStack rejects attaching a
> seventh data volume.
> Friðvin Logi Oddbjörnsson
> Senior Developer
> Tel: (+354) 415 0200 | <>
> Mobile: (+354) 696 6528 | PGP Key: 57CA1B00
> <
> Twitter: @greenqloud <> | @qstackcloud
> <>
> |
> [image: qstack_blue_landscape_byqreenqloud-01.png]

Rafael Weingärtner

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