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Re: [lvm-devel] [PATCH V2 0/2] Add thin lv and thin pool creation support



Tony Asleson <tasleson redhat com> writes:

> On 01/31/2013 08:25 AM, M. Mohan Kumar wrote:
>> From: "M. Mohan Kumar" <mohan in ibm com>
>> 
>> Add thin lv and thin pool creation support to lvm2app.
>> 
>> Changes from previous version:
>> * Add support to specify data block size and low water mark thresold for
>> newly created thin pool.
>> * Added support for specifying lowwatermark parameter to thin pool
>> creation in lvcreate command
>
> OK, so the block size if specified as 0 results in a default value being
> selected as before, which is what I believe we want.  The default low
> water mark was 0, which is what we believe disables event creation.
> This doesn't appear to be a safe default behavior?
>
> One option would be to change the type to a signed integer and change
> the meaning from number of blocks free to percentage free and then treat
> -1 as pick a sane default.  Thus 0 would be no events and 30 would
> indicate when 30% blocks free is remaining to generate an event.  We
> could also use an unsigned value and use 100 as please pick a sane
> default as this value and values close to it really wouldn't make much
> sense.

IMHO specifying the % in threshold is a good idea. You suggest to assume some
default threshold for newly created thin pool if user is not passing
anything. May be we can document this in lvm2app.h mentioning if '0'
passed as percentage it will be treated as the default thresold and 100%
means no event will be generated. What do you think about this policy?

>
> Once we have defined what the default values are, I can modify my python
> bindings patch to use these default values.
>
> Thanks,
> Tony


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