Re: [RFC] Btrfs "sendshots" and hidden snapshots

[Goffredo Baroncelli <kreijack@libero.it>]

On 07/06/2012 10:51 AM, Alexander Block wrote:
> On Fri, Jul 6, 2012 at 12:34 AM, Goffredo Baroncelli <kreijack@libero.it> wrote:
>> On 07/05/2012 06:51 PM, Alexander Block wrote:
>>> Hello all,
>>>
[....]
>>> When we later do an incremental send we can do this:
>>> 1. Do the same as point 1. from above.
>>> 2. Determine which of the previous sendshots is the correct one for
>>> the incremental send. We could use some magic auto detection here or
>>> the user has to specify it by himself.
>>> 3. Use the hidden snapshot from 1. and the determined sendshot from 2.
>>> to find the incremental changes and do the send.
>>
>> I can understand how a sendshot could be used to compute the metadata
>> delta. But how compute the data delta ?
> We still would have the file extent data found in the metadata. When
> we see that logical addresses or generations have changed, we know the
> data has changed. This may however be problematic in case a defrag or
> balance was performed, for this we should probably introduce a data
> only transid or something like that which is preserved on such
> operations.

Yes, this makes sense. The data that has to be collected is only the new
one, if I can track which data is changed (comparing the extent data )
then I need only the new data.

>>