[dm-devel] dd between thin provisioned devices

[devicemapper niko]

thanks for the reply. What i really wanna to ask is thin clone/mirror
supported or not.

I noticed the time later SCSI commad GET LBA STATUS can fullfil this
requiremnt .

Before block copy, send GET LBA STATUS to check the corresponding blocks
mapped or not.
if not, just skip copy.


On Mon, Jan 28, 2013 at 5:06 PM, Zdenek Kabelac <zdenek.kabelac at gmail.com>wrote:

> Dne 27.1.2013 11:01, devicemapper niko napsal(a):
>
>  Hi,everyone
>> if we dd between thin provisioned devices,
>> can we just get allocated blocks copied ?
>>
>
> Nope - devices mapper target operates on block level - not on the
> filesystem
> level - so it has no knowledge about file layout.
>
> What I could eventually imagine is some kind of block compactification
> (just like kernel does for hugepages) - but it's currently not being
> developed....
>
>
>
>  Will the output thin device get fully provisioned?
>> I glanced through the dm-thin code,
>> it turns out unmapped blocks return zeroed,am i right?
>>
>
> depends on settings - you could have either zeroed block or block
> with content left on the disk - i.e. running thin with 1MB block/chunk size
> means - before the first use whole 1MB must be zeroed - so it has its
> price.
>
>
>  Is there a trick to tell upper applications that all u got are zeroes.
>> or should they scan zeroed blocks themselves to trigger WRITE_SAME to
>> reduce
>> I/O load?
>>
>
>
> Documentation/device-mapper/**thin-provisioning.txt
> see flag: skip_block_zeroing
>
> Eventually for lvm2   lvcreate --zero y|n for thin pool creation.
>
> Zdenek
>
>
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