openstack/cinder
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api-ref: add multiattach considerations to retype docs

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This adds some notes about two things to consider with a volume
retype operation on an in-use multiattach volume:

1. The volume API will reject a retype operation on an in-use volume
   where the volume's multiattach value would change.

2. Retyping an in-use volume that has more than one active read/write
   attachment is not recommended because on the nova side the swap
   volume operation performs a blockRebase which could potentially
   lead to data corruption.

In the future, we (nova or cinder or both) will likely need to make
some changes as to what the default attach_mode is for secondary
attachments to a multiattach volume, since today we default to read/write
if it's not specified by the caller when making the attachment.

Change-Id: Ib5a2830ea3cd37236947677225252ef42edaa347
This commit is contained in:
Matt Riedemann 2018-01-25 13:48:05 -05:00
parent 76f2158d47
commit 2e1d31a44a
2 changed files with 10 additions and 0 deletions
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5
api-ref/source/v2/volumes-v2-volumes-actions.inc
View File

@ -340,6 +340,11 @@ Change type of existing volume. Specify the ``os-retype`` action in the request
Change the volume type of existing volume, Cinder may migrate the volume to
proper volume host according to the new volume type.
Retyping an *in-use* volume from a multiattach-capable type to a
non-multiattach-capable type, or vice-versa, is not supported. It is generally
not recommended to retype an *in-use* multiattach volume if that volume has
more than one active read/write attachment.
Policy defaults enable only users with the administrative role or the owner of
the volume to perform this operation. Cloud providers can change these
permissions through the policy.json file.

5
api-ref/source/v3/volumes-v3-volumes-actions.inc
View File

@ -369,6 +369,11 @@ Change type of existing volume. Specify the ``os-retype`` action in the request
Change the volume type of existing volume, Cinder may migrate the volume to
proper volume host according to the new volume type.
Retyping an *in-use* volume from a multiattach-capable type to a
non-multiattach-capable type, or vice-versa, is not supported. It is generally
not recommended to retype an *in-use* multiattach volume if that volume has
more than one active read/write attachment.
Policy defaults enable only users with the administrative role or the owner of
the volume to perform this operation. Cloud providers can change these
permissions through the policy.json file.