[Gluster-devel] autodelete in snapshots

[M S Vishwanath Bhat]

On 3 June 2014 01:02, M S Vishwanath Bhat <msvbhat at gmail.com> wrote:

>
>
>
> On 2 June 2014 20:22, Vijay Bellur <vbellur at redhat.com> wrote:
>
>> On 04/23/2014 05:50 AM, Vijay Bellur wrote:
>>
>>> On 04/20/2014 11:42 PM, Lalatendu Mohanty wrote:
>>>
>>>> On 04/16/2014 11:39 AM, Avra Sengupta wrote:
>>>>
>>>>> The whole purpose of introducing the soft-limit is, that at any point
>>>>> of time the number of
>>>>> snaps should not exceed the hard limit. If we trigger auto-delete on
>>>>> hitting hard-limit, then
>>>>> the purpose itself is lost, because at that point we would be taking a
>>>>> snap, making the limit
>>>>> hard-limit + 1, and then triggering auto-delete, which violates the
>>>>> sanctity of the hard-limit.
>>>>> Also what happens when we are at hard-limit + 1, and another snap is
>>>>> issued, while auto-delete
>>>>> is yet to process the first delete. At that point we end up at
>>>>> hard-limit + 1. Also what happens
>>>>> if for a particular snap the auto-delete fails.
>>>>>
>>>>> We should see the hard-limit, as something set by the admin keeping in
>>>>> mind the resource consumption
>>>>> and at no-point should we cross this limit, come what may. If we hit
>>>>> this limit, the create command
>>>>> should fail asking the user to delete snaps using the "snapshot
>>>>> delete" command.
>>>>>
>>>>> The two options Raghavendra mentioned are applicable for the
>>>>> soft-limit only, in which cases on
>>>>> hitting the soft-limit
>>>>>
>>>>> 1. Trigger auto-delete
>>>>>
>>>>> or
>>>>>
>>>>> 2. Log a warning-message, for the user saying the number of snaps is
>>>>> exceeding the snap-limit and
>>>>> display the number of available snaps
>>>>>
>>>>> Now which of these should happen also depends on the user, because the
>>>>> auto-delete option
>>>>> is configurable.
>>>>>
>>>>> So if the auto-delete option is set as true, auto-delete should be
>>>>> triggered and the above message
>>>>> should also be logged.
>>>>>
>>>>> But if the option is set as false, only the message should be logged.
>>>>>
>>>>> This is the behaviour as designed. Adding Rahul, and Seema in the
>>>>> mail, to reflect upon the
>>>>> behaviour as well.
>>>>>
>>>>> Regards,
>>>>> Avra
>>>>>
>>>>
>>>> This sounds correct. However we need to make sure that the usage or
>>>> documentation around this should be good enough , so that users
>>>> understand the each of the limits correctly.
>>>>
>>>>
>>> It might be better to avoid the usage of the term "soft-limit".
>>> soft-limit as used in quota and other places generally has an alerting
>>> connotation. Something like "auto-deletion-limit" might be better.
>>>
>>>
>> I still see references to "soft-limit" and auto deletion seems to get
>> triggered upon reaching soft-limit.
>>
>> Why is the ability to auto delete not configurable? It does seem pretty
>> nasty to go about deleting snapshots without obtaining explicit consent
>> from the user.
>>
>
> I agree with Vijay here. It's not good to delete a snap (even though it is
> oldest) without the explicit consent from user.
>
> FYI It took me more than 2 weeks to figure out that my snaps were getting
> autodeleted after reaching "soft-limit". For all I know I had not done
> anything and my snap restore were failing.
>
> I propose to remove the terms "soft" and "hard" limit. I believe there
> should be a limit (just "limit") after which all snapshot creates should
> fail with proper error messages. And there can be a water-mark after which
> user should get warning messages. So below is my proposal.
>
> *auto-delete + snap-limit:  *If the snap-limit is set to *n*, next snap
> create (n+1th) will succeed *only if* *if auto-delete is set to on/true/1*
> and oldest snap will get deleted automatically. If autodelete is set to
> off/false/0 , (n+1)th snap create will fail with proper error message from
> gluster CLI command.  But again by default autodelete should be off.
>
> *snap-water-mark*: This should come in picture only if autodelete is
> turned off. It should not have any meaning if auto-delete is turned ON.
> Basically it's usage is to give the user warning that limit almost being
> reached and it is time for admin to decide which snaps should be deleted
> (or which should be kept)
>
> *my two cents*
>
Adding gluster-users as well.

-MS

>
> -MS
>
>
>>
>> Cheers,
>>
>> Vijay
>>
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>
>
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