filesystem type storage backend

[Andrew Wilkins]

On Sat, Feb 6, 2016 at 2:30 AM Marco Ceppi <marco.ceppi at canonical.com>
wrote:

> This sounds very promising! Will play around with it a bit more.
>
> On Fri, Feb 5, 2016, 7:16 PM Mark Shuttleworth <mark at ubuntu.com> wrote:
>
>> On 05/02/16 17:47, Marco Ceppi wrote:
>> > Does this require the operator to add storage at deploy time? Does this
>> > mean our charm should block until storage is added? We really want to be
>> > able to support the /option/ or adding storage by the operator but we're
>> > not sure how this functions. If we use that directory before the
>> operator
>> > attaches storage will it be mounted over or migrated?
>>
>> AIUI:
>>
>>  * you can leave the storage unspecified and it will just write to the
>> directory
>>  * you cannot change the storage pool after deployment
>>
>
Correct on both counts. If you don't specify storage, Juju will just create
"/srv/hdfs" on the root filesystem, and you cannot change this after
deployment.

Furthermore: the charm's install hook will not fire until the storage is
available and attached (which means "-storage-attached" hooks will fire
before "install"). So you know, at charm install time, the storage is
there; no need to block, Juju is doing that for you.

It's worth noting that it is also possible to make make storage optional by
setting the minimum number of storage instances to 0, like so:

storage:
    hdfs-data:
        type: filesystem
        location: /srv/hdfs
        multiple:
            range: 0-1

If you deploy such a charm without specifying a storage directive, you will
get no storage. If you do want the storage, you either deploy with
--storage, or use "juju storage add" (juju add-storage in 2.0, I believe).
IIRC, if the specified location already exists, and is non-empty, Juju will
refuse to mount the storage over the top.

Cheers,
Andrew

Mark
>>
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