Re: snapshot-removal - timeline ?

[Andrey Kuzmin <andrey.v.kuzmin@gmail.com>]

On Wed, Aug 5, 2009 at 10:46 PM, Christian Mikovits<gaelic@luchmhor.net=
> wrote:
> I guess whats really hard to program: snapshot removal when not
> copying the data, but only pointing to that data and writing the
> differences from that point on. Figure out how difficult it is to
> remove snapshot 3 of 7; When snapshot 1 is the original data, snap2
> the diff from 1 to 2, snap 3 the diff from 2 to 3, .... so you have t=
o
> merge the data of snap 3 and 4.

Depends on the snapshot design: if snapshots are implemented with
reference counts, nothing needs to be merged (but simplicity in this
respect comes at the cost of garbage collection).

Regards,
Andrey

>
> But the benefits are obvious: instant snapshots and very low space
> consumption (in case you don't delete lots of your 'live' data).
>
> On 8/5/09, Andrey Kuzmin <andrey.v.kuzmin@gmail.com> wrote:
>> On Wed, Aug 5, 2009 at 3:18 PM, Roy Sigurd Karlsbakk <roy@karlsbakk.=
net>
>> wrote:
>>>
>>> On 4. aug.. 2009, at 20.33, Chris Mason wrote:
>>>
>>>>> It's strange that such a small thing should be delayed so much. I=
f
>>>>> snapshot removal was working, I'm quite sure we might get more us=
ers
>>>>> and thereby more stable code faster.
>>>>
>>>> It's a small feature but it gets deep into the difficult parts of =
the
>>>> dentry cache to do it right. =A0So, it definitely isn't easy.
>>>
>>>
>>> I'd say it's a pretty elemetary feature to be able to remove someth=
ing you
>>> have created.
>>
>> Snapshots are somewhat counter-intuitive in many respects: for
>> instance, one snapshot-capable file-system performs writes to =A0a
>> dataset with snapshots _faster_ than to the same dataset w/o
>> snapshots. Snapshot removal is no exception - it's a bit more comple=
x
>> than one would think.
>>
>> Regards,
>> Andrey
>>
>>> I know, you can remove the files and so on, but still, having a bun=
ch of
>>> old and empty
>>> snapshots lying around is no good.
>>
>>
>>>
>>> roy
>>> --
>>> Roy Sigurd Karlsbakk
>>> (+47) 97542685
>>> roy@karlsbakk.net
>>> http://blogg.karlsbakk.net/
>>> --
>>> I all pedagogikk er det essensielt at pensum presenteres intelligib=
elt.
>>> Det er et element=E6rt imperativ for alle pedagoger =E5 unng=E5 eks=
essiv
>>> anvendelse av idiomer med fremmed opprinnelse. I de fleste tilfelle=
r
>>> eksisterer adekvate og relevante synonymer p=E5 norsk.
>>>
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