Re: [Gluster-devel] autodelete in snapshots

[Rahul Hinduja]

----- Original Message -----
> From: "Avra Sengupta" <address@hidden>
> To: "Lalatendu Mohanty" <address@hidden>, "Raghavendra Bhat" 
> <address@hidden>, "gluster-devel"
> <address@hidden>, "Rahul Hinduja" <address@hidden>, "Seema Naik" 
> <address@hidden>
> Sent: Wednesday, April 16, 2014 11:39:11 AM
> Subject: Re: [Gluster-devel] autodelete in snapshots
> 
> 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.

Agreed with Avra, the purpose of introducing soft limits and hard limits was to 
restrict snap creation to reach limit+1 at any point in time. Any time the 
limit reaches the hard limit the subsequent creation should fail. Once the 
limit reaches the soft limit the auto-delete starts in background. Since 
soft-limit is configurable option between 1-100, it really gives flexibility to 
the user to start the auto-deletion based on his requirement it can be at 1% or 
even 100% soft-limit.

If the auto-delete option is set to true than it should be triggered and should 
log message based on user's input of soft-limit and if it is set to false the 
auto-delete should only log message and snap creation fails when it reaches the 
hard-limit.

Thanks,
Rahul

> 
> Regards,
> Avra
> 
> On 04/15/2014 07:18 PM, Lalatendu Mohanty wrote:
> 
> > On 04/15/2014 07:05 PM, Raghavendra Bhat wrote:
> >>
> >> Hi,
> >>
> >> As of now, in snapshots there are 2 limits for the number of
> >> snapshots, hard-limit and soft-limit. Usually soft-limit is 90% of
> >> hard-limit by default (it can be changed also). Say the hard-limit is
> >> 50, then soft-limit by default will be 45. We are planning to do
> >> autodelete of the oldest snapshot upon reaching the limit.
> >>
> >> There are 2 options:
> >>
> >> 1) Start doing autodelete upon reaching the soft-limit. i.e If the
> >> hard limit is 50 and the  number of the snapshots taken becomes 45,
> >> then for the next snapshot taken (i.e 46th snapshot), the oldest
> >> snapshot will be automatically deleted in the background.
> >>
> >> 2) Use soft-limit as a means to notify the admin about limit being
> >> reached (gf_log, syslog etc, or also a warning message shown for
> >> every snapshot taken after the soft limit is reached) and start doing
> >> autodelete after reaching the hard-limit i.e once 50 snapshots are
> >> reached, then when 51st snapshot is triggered, the oldest snapshot
> >> will be deleted in the background.
> >>
> >> Please provide feedback.
> >
> > I like the #2 option. If user has set something as hard-limit, it
> > should be treated as hard limit and soft-limit can be used as warning
> > mechanism.
> >
> >>
> >> NOTE: The auto-delete can be made configurable, which if turned off,
> >> snapshot create fails upon reaching the limit.
> >>
> >> Regards,
> >> Raghavendra Bhat
> >>
> >> _______________________________________________
> >> Gluster-devel mailing list
> >> address@hidden
> >> https://lists.nongnu.org/mailman/listinfo/gluster-devel
> >
> >
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